I'm thinking about about constructing a compartment in the under bed storage, but I'm not sure I want the stink in the bedroom. I guess I could add an exhaust fan with a charcoal filter. 

One of the first mods we did in our 178 was cat head (head as in litter box space). See pics in my signature link. It was in "the bedroom" and essentially under the bunk. We have traveled 10's of thousands of miles; first with Henry the camping cat and now with Theo the extraordinary camping cat. It has worked wonderfully. I must say that my wife is amazing @ litter box duty. Odor has never been an issue.

Anecdotally, we carry a separate lidded litter box in the back of our TV. Henry was and Theo is a great traveling cat. Theo rarely uses the box while in TV and she is strangely almost odorless . Henry was not shy at all about using it and, yes, there was a time or two we had to pull off the side of the road, clean the box, open the windows and wonder what the hell he ate!! I sorta admired that.

fred

Co-pilot => Henry  R.I.P

Are We There Yet => Theo

I'll check that out.

I simply added a cat door under the table:

Then put the litter box right next to the cabinet door for easy access to empty:

If the weather is bad I use this door, but it is more convenient to use the outside door for emptying.

Kiki loves the set up:

Kiki's got some cool markings. Looks like a hunter and reminds me of our Henry (rip).

Do you use the same box in your TV? 

fred

Fred,

No picture of it but I use a fully covered box on the back seat floor of the truck.  Keeps the odor down.  The seats are all covered to keep the litter crumb clean up to a minimum.  She loves to travel and even snoozes in the Pod when it's in the driveway.