Replace instant hot with standard water heater?

I feel like I'm being pushed into a corner where I'll have to purchase an RV with an instant hot water heater, and I don't like it. I already grumbled about it in the Travel Trailer forum.

I know this goes against the grain of the typical questions asked here, but I'm curious if anybody has ever swapped back to a conventional water heater. Is it difficult? How do the installed dimensions compare?

Thoughts and ideas welcome!