Has anyone replaced a hot water tank with an instant hot?

I'm in the same boat regarding not using the water heater much at all. I do test it each year to make sure it's functioning, but don't really use it. Never really thought of going the instant hot water route as I agree that the current water heater does a fine job when needed. Most trips i run with it empty so not carrying the weight. The only need I have for hot water is doing the dishes so I just heat up some water in a pot on the stove and dump it in the sink. Heats up quick and only the amount I need, not six gallons.
I have heard of others changing to instant hot water so I would assume size wise it should fit just fine in the same spot your current heater is.

I installed the "Hot Rod" electric conversion in my 6 gallon tank. I like it. When the RV is plugged in, my water is hot without firing the LP! Most of the on demand heaters have a large electric or gas pull to heat the water on demand.
Brian

What do you seek to improve? The current water heater is there and works just fine as-is, right? At no extra cost.

Instantaneous heaters usually need a short time to reach the desired output heat - some extra water is probably wasted that way.

Usually, fresh water is a more limited resource when traveling than LPG.

You would also reduce your fresh water reserve by the 6 gal. in the boiler tank.

In winterizing it might save a few minutes.