I used Krylon Farm and Implement Paint on my 42 year-old Lund. I added their catalyst hardener when I painted.
Prep of the surface is important. I used a polycarbide abrasive disc in my angle grinder to strip and clean the surface to be painted. Make sure you spend the time to get it clean, and then wipe down the area to be painted with acetone to remove all residue.
Krylon's web site does indicate that it can be applied direct to metal, but a good primer is probably a great idea. I didn't and have had no issues to date, but this is the first full season since I painted last July.
The quart of Krylon that I bought was enough to paint my 14' aluminum boat, with some left over.
Use a respirator with appropriate cartridges...it's strong stuff.
I rolled and tipped it with a brush; actually looks fairly decent. It's hard stuff. It calls for 72 hours of dry time, but I left mine alone for two full weeks before I applied registration numbers and period-correct Lund decals.
Between paint, hardener, abrasives, and miscellaneous stuff, I spent less than $60 on the whole thing.
