Re: Interior Painting ????
We went through this fairly recently. Use plain old acrylic kitchen & bathroom semi gloss. It has some mildewcides in it and it is tough and damp resistant. I've used it with great success several times.
Don't waste your money on marine or specialty coatings - they aren't necessary and won't do anything extra for you.
As to prep - yes, sand it. If you have exceptionally heavy glass weave showing, like 24 Oz. roving, you may want to use a plastic or brass "wire brush" in a drill or angle grinder to clean out the low spots.
Use Bilge Kote or barrier coat in your bilges, not paint.
I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.