Tankless water heater

Truman AquaGo is what you want. It's made to replace the 6 or 12 gal Atwood in the typical fiver.

Can't think of the name now but there is a new one that has a bypass system so the water in the piping is always hot.
BUT unless your rig is in a permanent spot I can't see any advantage to going tankless. It's an RV!
Truman AquaGo as posted below. Yes, named after the former President.

Make sure you have plenty of water pressure, otherwise the system won't work like you expect. Do a search and you will find where folks regretted the tankless or demand system.

When we ordered our 2019 Cedar Creek, we opted for the 12 Gal propane/electric tank.

Moved from class C.