No experience here with tankless other than I set one up for my daughter's horse trailer. It is a temporary installation and requires disconnecting and stowing when not using, originally designed to be hung on a tree as a camp shower.
If you go tankless, can you use both electric and LP? I would think finding an electric element that could heat water that quickly would require a lot of amperage. If you have to use just LP is that a problem?
I like the idea of tankless when it comes to winterizing, looks like it would be a lot easier than draining, flushing and bypassing.
Denny, Connie & Shadow (former barn cat made good)
2000 Itasca Horizon, Cat 3126B, Freightliner Chassis