First thing I would do is check the actual hot water temp. It sounds to me as if you are not getting a typical hot water temp, cause most of the hot water temps I've encounter are extremely high in RV's. Easily 130, and I believe more like 140 as previously mention.
If you want an endless supply of hot water, look for electric "point of use" tank-less options. We often camp with a family of 4 who installed a 20amp (electric) Bosche 4gpm "point of use" unit for less than $200. While they are made for one typical home end point (faucet) and rated for only 4gpm, its the perfect flow rate and temp rise for RV's. They rave about it.
I don't know if this is common in the RV world or not, I never looked. There may be downsides that I am not aware of. I'm years away from actually needing to think about it.