well... first you need the gel coat, then the catalyst then the top coat additive and wax(depending on brand).. gel coat is meant to be used as an airless cure, meaning it's the outermost layer on the part.. when it's in the mold it's the innermost layer, between the mold and the glass/smc/carbon... i hate the way it sprays through an hvlp(1.4).. base/clear auto paint is much more readily available on a local basis.. it's hard to compare the difference between them.. cost wise about the same, procedure time clear would be quicker and less technical yet it's still pretty involved for someone who doesn't know about it... i mix clear on a daily basis so it's more than second nature to me, some days i think i should have a chemistry degree, look in my paint room and you'll be lost in .3 seconds... base coat is mixed 1:1 with reducer, clear is 4:1:1 with catalyst and reducer, surfacer is 4:1:1 with another catalyst and reducer, sealer is 3:1:1 with yet another catalyst, epoxy is 2:1 with another catalyst... haha that's just the surface.. anyway..
some clears are 4:1(no reducer) that's what i would suggest to anyone not familiar(omni "quick clear" comes to mind) gel coat requires mekp(methyl ethyl ketone peroxide) same catalyst you use is your resins.. you don't "need" to add wax, just have to block it from air contact for full cure.. thing is, i'm not sure how well gel coat will adhere to unsanded paint, i've only used factory match color coat(on boat repairs), not clear gel(i was going to do my sj with gel when i painted this past winter, but decided not to since i already have clear on hand... really, it's a horse a piece, they'll both hold up, gel reacts more to heat than clear.. i honestly think clear will hold up better for this reason, but they use it from the factory just because the process of molding composites... sorry this was so drug out, but they're strong and weak points are so close together it comes down to personal preference... gel is just a little more involved..