Installed first tankless 37 years ago. Main advantage of them is that you can put them almost anywhere, what is crucial in small condos.
The older, with pilot gave you hot water without waiting, but then wasted gas when seldom used.
New, electronic technology saves energy by not running pilot, but waste water as you have to wait for the system to run the igniting process.
Main problem with them is that people buy smaller output than they need.
With undersized unit, in cold weather the flow is very small as there is not enough heating power.
Had big tankless in previous house and could not imagine anything else with 60 gallons whirlpool tub.
From what I read, RV tankless are still not very reliable, so you'll be Guinea Pig in testing them.
I ditto on using electric element on traditional RV heaters whenever you can.
I add such element to our 5 gallon heater when we fulltimed last winter and we could take 2 showers back to back just fine.
Electric element not only will give you higher temperature, but being lower than propane burner - will heat whole tank, not only upper part like propane.