Re: the starcraft islander rescue.....sorta.....got some work ahead!
Yeah, the guys at HD wouldn't be my 1st resource, paint department or not.
If you sand to BARE aluminum hull, give it a quick acid wash (50/50 vinegar & water) bath and rinse w/ plain water. Dry, then use SE (self-etching) or ZC (zinc chromate) only on the bare aluminum areas only, and only a sparse coating of the SE/ZC. Then prime the ENTIRE hull, preferably w/ primer from the same paint line as your finish paint. A LIGHT sanding between coats, helps get a better final finish to your top coats.