I'm doing my damn taxes.
The thing that jumps out most of all is how expensive an automotive finish is. I sprayed my little One Man Dayak metallic blue last year. Twice. Because I fucked it up the first time so I had to sand it and spray it deja vu all over again. Holy cow. I must have spent a good $600 on boat paint last year. For one small boat. That's about what I had in Plascore and fiberglass for that boat.
Next time it's back to Petitt Easy Poxy. $40 per quart. Two quarts'll do ya. With left overs to touch up with later on. You can't save anything with automotive paint because it's a two part mix you have to toss, if anything is left over. Throw in primer and thinner and sand paper and Petitt is still less than $150. Paint thinner is $15 a gallon. Automotive reducer is $50 a gallon.
I used to say good things about oil based house paint, which costs $45 per gallon. But it is soft and very easily scratched. Petitt (and a few others like it) are substantially tougher, and clearly the best compromise.
I don't know about the real chemical differences, but house paint is "alkyd" paint. Petitt is a one part polyurethane. Two part marine and automotive finishes are two part catalyzed polyurethanes. They're the best. But not so much as a cost/benefit ratio. The two part paints are too expensive for me. I'm over it.
..........also, and finally. I have a $600 LPHV Fuji sprayer. So I use it. Even with Petitt paints. But Petitt paints can be rolled on and brushed out by hand (aka rolled and tipped), Two part polyurethanes must be sprayed. No two ways about it.