Bathroom Remodel Question ~> Full size tub/shower combo?

I'd be concerned about the weight. Not of the plastic tub, the water. At 8.3 pounds per gallon, you could wind up soaking under your RV instead of in it. That's not only expensive, its embarrassing. :)
My parents were RVers. After many years and miles, they decided to swap their 'C' for a park model in Florida. They're designed to support a shower/tub combo because they sit on a concrete slab and have a full size water heater. Sure made my Mom happy.