Tips on acclimating the family to longer road trips

Your question basically boils down to how much risk you're willing to tolerate. The added convenience of a MH over a 5er/TT is that passengers can and often will move about the cabin while in flight. Is it legal, safe or ethical? That's a debate that will rage until doomsday.

I can tell you that traveling in my MH has made long trips 1000% more enjoyable and less stressful for all of the reasons the OP alluded to in the original post.