Here are the facts, so you can make your own decision.

The 50A circuit at the campground has a circuit breaker on the pedestal that will trip at 50 amps. The trailer panel has a circuit breaker on it that will trip at 30 amps which will protect everything downstream of that. In between the dog bone and the breaker in the trailer panel is your cable with a connector on each end, a receptacle on the trailer, and wiring between that receptacle and the circuit breaker in the trailer, all of which is rated to handle 30A but not 50A. 

So, if you get a short in between the dog bone and the trailer circuit breaker that allows more than 30A to flow but less than 50A you can overheat the cable, connectors, receptacle, or wiring which could cause a fire. If the short is more than 50A the circuit breaker on the pedestal will trip. 

Because of this potential risk there is a label next to the trailer receptacle which says not to connect it to a circuit that can provide more than 30A. The plug protector you have protects from some other things but not from this particular risk. And the dog bone manufacturer is not responsible if there is a problem, they meet the requirements they need to meet to sell their product. its up to you how you use it. 

Is such a short circuit (less than 50A but greater than 30A) possible? Yes, I have seen similar shorts on other circuits but not on RV's. Is it common? Not at all, very uncommon on RV's if its happened at all. 

So, there you have it, up to you to decide what you're comfortable with based on your risk tolerance. 

Edit:  Maybe this??

https://www.etrailer.com/p-CAM55301.html - https://www.etrailer.com/p-CAM55301.html

https://itstillruns.com/run-amp-rv-50-amps-7717012.html - https://itstillruns.com/run-amp-rv-50-amps-7717012.html

So if this is correct and the dogbone actually steps the current down to 30 Amps right out of the pedestal, is there really any danger?

Ok...how about this:

From the 50A-to-30A dogbone you plug this in:

https://www.homedepot.com/p/AC-WORKS-1-5-ft-10-3-STW-30-Amp-TT-30P-RV-Travel-Trailer-Plug-to-30-Amp-L14-30R-2-Hots-Bridged-Adapter-TT30L1430-018/302447731?mtc=Shopping-VF-F_D27E-G-D27E-27_3_EXT_CORD_WORKLIGHT_SURGE-Generic-NA-Feed-PLA-NA-NA-EXT_CORD_WORKLIGHT_SURGE&cm_mmc=Shopping-VF-F_D27E-G-D27E-27_3_EXT_CORD_WORKLIGHT_SURGE-Generic-NA-Feed-PLA-NA-NA-EXT_CORD_WORKLIGHT_SURGE-71700000033101998-58700003865786276-92700048704092120&gclid=Cj0KCQiAvc_xBRCYARIsAC5QT9l8L6GnF6GVP4Vhik7aBpe004b-pk91twhStAIG1E1qAeCumkFjV30aArDuEALw_wcB&gclsrc=aw.ds - https://www.homedepot.com/p/AC-WORKS-1-5-ft-10-3-STW-30-Amp-TT-30P-RV-Travel-Trailer-Plug-to-30-Amp-L14-30R-2-Hots-Bridged-Adapter-TT30L1430-018/302447731

Then your RIGID adapter with 20-amp breaker

Then this:

https://www.homedepot.com/p/AC-WORKS-RV-Generator-Adapter-NEMA-L14-20P-20-Amp-125-Volt-250-Volt-4-Prong-Locking-Plug-to-RV-TT-30R-30-Amp-RV-Female-Connector-RVL1420TT/301828763 - https://www.homedepot.com/p/AC-WORKS-RV-Generator-Adapter-NEMA-L14-20P-20-Amp-125-Volt-250-Volt-4-Prong-Locking-Plug-to-RV-TT-30R-30-Amp-RV-Female-Connector-RVL1420TT/301828763

Then the RV's power cord.

Thoughts?

Hmmm...maybe an electrician could put something together, assuming that 30A breakers that could be wired inline actually exist.

Could one pull the breaker out of this and use it somehow, or possibly wire a 50A connector to the backside?

https://www.homedepot.com/p/Connecticut-Electric-30-Amp-RV-Power-Outlet-with-30-Amp-Single-Pole-Breaker-CESMPSC13HR/100430208 - https://www.homedepot.com/p/Connecticut-Electric-30-Amp-RV-Power-Outlet-with-30-Amp-Single-Pole-Breaker-CESMPSC13HR/100430208

ETA:  Here's just the breaker:

https://www.homedepot.com/p/Square-D-Homeline-30-Amp-Single-Pole-Circuit-Breaker-HOM130CP/202353319 - https://www.homedepot.com/p/Square-D-Homeline-30-Amp-Single-Pole-Circuit-Breaker-HOM130CP/202353319

If you bought a separate breaker and mounted it in a NEMA 4X watertight enclosure and used water tight cable glands to bring the cables out that would be better. The breaker you picked wouldn't work though, its designed to snap onto the bus bar in a home panelboard. You'd need to find a back mount breaker and attach it to a back plate in the 4X box. 

If you're worried about having nuisance trips of the 20A inline breaker, I can say that I've run my trailer on a 20A circuit at home a lot and have never had the breaker trip.  Although I haven't tried to run the microwave and the a/c simultaneously, its not a big deal to turn off the a/c for a few minutes when running the micro, I have to do that when running on my Honda 2K genny.

Ok, fair enough.

Do you think that having five devices between the pedestal and the RV poses an undue risk?

OTOH, don't be afraid to change out your connectors,  it really isn't hard. If you've ever reterminated a cord, its the same kinda thing. 

When I said leave one of the hots disconnected on the 50A 240V connector, don't let that confuse you.  The two hots are the pins opposite each other side to side, the neutral and ground pins are opposite each other top and bottom.The ground pin is the round one. You get 240Vac between the two hots and 120Vac from either hot to neutral.  Since you only want 120Vac out, one hot is unused. 

When you cut off the cable on the Rigid part, you will see a green, a white, and a colored wire (usually black but sometimes red).  So, you connect green to the ground pin, white to neutral pin, and the colored wire to one of the two hot pins. Doesn't matter which. The other hot pin will be unused. That will give you 120Vac out same as the dogbone does.

On the output connector looking at the end face of the female receptacle with the round hole up, the neutral is the pin on the right and the hot is the pin on the left. So, white to neutral, black (or red) to hot, green to ground, same as before.

You're probably right.  However, it's interesting to Google something like "Are 50A-to-30A dogbones safe?" because the answers/opinions are all over the lot, with a smattering of self-professed electrical geniuses (some of whom likely know what they're talking about) saying don't use them under any circumstances, and most folks being pragmatic and echoing what you say, based on the empirical evidence.

1) I have seen the type of current limited fault conditions that is the risk here, more than once. Not on RVs but in other electrical systems. They are nasty and dangerous, and there is noting different about RVs that would preclude those same type of faults there. 

2) It goes against a fundamental principal of electrical safety design not to properly protect all circuits from current overloads. 

3) The national electric code making panel for article 551 (which covers RVs), who are not dummies, feel its enough of a risk to require RV manufacturers to place a label warning against doing exactly this next to the RV power inlet. 

So, I'm not personally gonna use one of those dog bones. 

As to the chances of being killed by a meteor, NASA puts that at about 1:250,000, compared to about 1:160,000 of being killed by a lightning strike, 1:3.7 million of being killed in a shark attack, and 1:292 million of winning the Powerball jackpot. So, not so far fetched as you might think. The big risk from meteors isn't getting directly hit by a little one, its a big one like the 1908 Tunguska event whacking a whole city or a huge planet buster like what took out the dinosaurs. 

Your experience and logical approach to this issue carries a lot of weight with me, which is why I've taken the time to explore options.  Thank you.

BTW, you really can't get whacked by a meteor unless you're out in space; once they hit Earth they become meteorites 

Its not a big hardship for me not to use one though. I very rarely camp where there is electricity. I certainly can see why those who do camp with hookups feel its a necessity. 

I might make up a current protected dog bone now though, as it looks like it can be done for about $35. If I do I'll report it here. 

I stand corrected about meteors vs meteorites.  

Cottage industry?  I'll be your first customer.

Especially if their ads featured a TT going up in flames...  "DON'T LET THIS HAPPEN TO YOU!!!!!!"

Wonder how common this is.

Hmmm...they (GetWiredUSA) advertise custom orders.

Edit: I asked if these are waterproof and if they can be made with a 50A plug and 30A socket for RV use. It will be interesting to see what reply I get. When it comes in, then I will post the reply here.

There are both 50 (in) to 30(out) and 30 (in) to 50(out) dog bone adapters. The latter are for 50A RV's to use an older 30A pedestal. Some campgrounds don't allow those because they tend to overload the older campground electrical systems, even if an individual RV doesn't actually trip the 30A breaker in that pedestal 

The point is to be sure you know exactly what is being excluded from use.  

I think offgrid just started a new company...

SafeDogBones LLC.

After all the snow clears, of course. 

Well, so far I've heard crickets from these guys.  Has anyone heard back?

Three times.  No answer.  Not today, though.