One more thing to understand is that if they DO get a 240VAC unit connected and working, that it WILL NOT work on 30Amp service. It will ONLY work on 50A service. Depending upon which generator is in their RV, it most likely won't work on generator power either. So that means they will ONLY get hot water while connected to 50A service. No hot water while on the road, dry camping or 30A campsites.
In my opinion, I wouldn't put one in my RV. I have one in the house and the wife hates it. The rest of us are OK with it, but it IS different than having a full tank of hot water. I really don't think they'll be ANY space savings involved with a tankless install, either.
And if money is tight, I would think the closest standard replacement would be the cheapest route. Pulling new wire, breakers and such, plus any additional propane plumbing (line might have to be upsized?) and it will be time consuming and if you have to pay someone to do that, the $$$ will QUICKLY surpass what a standard replacement would cost.
Personally, I like our Propane/electric 10 Gallon heater in the RV. We've never had a hot water problem, though we all pretty good at water conservation. Well...except the teen age daughter! She tries! LOL
Good Luck,
~Rick
2005 Georgie Boy Cruise Master 3625 DS on a Workhorse W-22
Rick, Gail, 1 girl (27-Angel since 2008), 1 girl (22), 2 boys (23 & 20).
2001 Honda Odyssey, Demco Aluminator tow bar & tow plate, SMI Silent Partner brake controller.