One VERY lucrative little sideline I have has been replacing the injection molded polystyrene shower pans with glass. I've done three of them so far and they were all cracked in the same place. They simply are not made to be used.
On two of them, I had to replace plywood in the floor because (of course) there was no membrane of any sort laid underneath them in case they leaked. Combine that with leaking drains and you are begging for a major repair bill. You'll never drive past a gas station...or a dealer's service dep't...
If you can buy a new bathtub and seat for $150, you have to wonder just how much profit there is in the RV manufacturing biz given what they charge for such a shoddy product.
I've installed a bunch of satellite systems in them and can also attest to what Bogo said about the walls. Next to trying to find a way to make the installation inconspicuous when the walls were built in place, reinforcing the 1/8" paneled walls to hang a TV is often a chore.
Once you pull the cover plate off an outlet or the antenna booster (to access the built in coax to the roof rather than drill and seal a new hole), it often looks like the aforementioned monkeys bashed to hole through with a hammer - the hole is irregular and the veneer on the paneling is blown out.
Still....RV owners seem content to pay over and over again to repair things that shouldn't need to be repaired. For a while I considered going to work for the local RV service shop, but thought better of it - I don't want to be part of that. I'd rather stick to boat work (not that you don't see shoddy work there too sometimes, it's just not as common)
The idea of reworking a bus or commercial truck has always appealed to me: you are starting with a product that was designed from the start to be robust and run darn near forever with regular maintenance.