Hi Tom, we have heard from people here that have roller hitches and have never rolled them. We have a Superglide automatic hitch in our shortbed Dodge truck, it works wonderfully. As for a non slider it would depend on where it was mounted, the design of the hitch and your truck axle
placement. I have heard of people mounting a non sliding hitch a few inches to the rear of "normal" mounting to gain turning space.
Replacing the water heater should be easy enough if you have some DIY skills. In our 5th wheels it is located under the bathroom fiberglass unit making the connections a bit challenging to reach.
As for "fitting" you need to see what your bed side measurement is and see what the hitch height and under the overhead measure on the trailer you are looking at. Comparing those things will let you know if it will hitch to your truck as is and have bedside clearance issues.
As for flipping the axle
it depends on how it is already mounted. Many have been modified in the passing years. Dual axle Bigfoots stock ride is pretty low!
Hope that helps.