Ac fan motor loose

We have a 2018 RPOD 179 with a DOMETIC 13,500 BTU AC. Our first trip was to Newfoundland, summer of 2019, did not use the AC much. Upon returning to the US, we began to notice a rattle noise in the AC when used. When we returned to Florida, took it to the dealer as it was covered under warranty. Allegedly repaired it.

We had planned to return to Newfoundland this year but due  COVID 19 it was impossible, so we are cruising thru the south. After a few state park the AC began to rattle again, I could reach up thru the duct and actually move the fan motor and it would stop. Only to start rattling again when we reached our new camp site. We finally able to get on the roof and remove the AC cowling, and discovered that both bolts that held the fan motor in place had vibrated out. Our fix was to reinsert bolts with lock tight on the threads, hopefully this will do the trick. Fan motor is not rattling at this time.

I am wondering what causes the screws to back out? Is the RPOD bouncing around to much? Poor design of the AC? Poor workmanship of the AC?

We cruise around 63 mph on the freeways and about 5 mph under posted speeds. Really slow on dirt roads, ets. No rush no hurry.