Being in the RV Service industry along with my own experience maybe I can give my two cents worth.
Tankless Systems are very progressive and new technology but some factors for proper operation are 1) Your propane system from tank to water heater must be in optimum condition especially the tank to regulator hose and the regulator.
2) In almost every case, priming the hot water to the faucet uses a lot of water. This is mainly a concern when
dry camping as water conservation is important.
3). Due to the complexity of these systems there can be more issues.
I have installed many of these. In all cases these units always would have spikes in delivered water temperature. This could result in cold and then hot showers etc.
The only on demand RV water heater which has accomplished solving this problem is the Truma line. Their products are outstanding.
They have the Aquago for side wall mounting in an RV but their Combi system installs inside the RV and not only provides tempered and steady water temperature but also heats the interior of the RV. It is very popular in Europe and is starting to make its way to North America. I believe the first trailer built in North America to get the Combi is from Airstream. The BaseCamp and soon to be released Nest.
It is perfect for small RV’s as you no longer have a water heater and
furnace. Just the Combi!