Before switching over to AGMs, just do the hot water/backing soda thing to remove the worst of the corrosion ... then sand a bit to get rid of any loose rust and old peeled paint. Finish up by just spraying color-matched Rustoleum paint (use the real stuff, not a knock-off) all over the area that used be covered with rust.
As you probably have picked up on regarding AGMs ... keep them undercharged the minimum amount of time you are able to when camping and when in storage ... whether your using a stock converter and/or an engine alternator. This works better than it does with standard batteries, because AGM batteries charge faster at any applied charge voltage.
All IMHO, of course.