this is how you *should* go about doing this.
do all your glassing, now you are ready for paint. sand the entire thing down so thers no burrs or any huge lumps\airbubbles anywhere (an angle grinder works great here).
now, take some bodyfiller or kittyhair and mix it up and lay it over your ENTIRE box, fill in all nooks and crannies, if you are using regular bodyfiller, do thinner layers at a time, do not go over 1\4" thick.
as this dries, it will turn to a hard\clay consistancy, if you got one, use a bodyfiller cutter (looks like a cheese grater) to get rid of any high spots or weird lumps just like you would do with a regular cheese grater.
then, wait until the bodyfiller completly hardens, and with 80~120 grit sandpaper (sorta rough) sand out the entire surface. (repeat this whole process on patches if its too low, and sand down anything that looks lumpy)
once it looks good, apply a skimcoat (thinned bodyfiller, you can buy this stuff, or you can just mix in a little acetone to your resin\mkep mixture and it turns into a toothpaste thickness, maybe thinner. smear this over the WHOLE THING. wait till dry.
sand this down with 200 grit or so till its smooth.
then take some high-build primer, and spray speckles from a distance (only a light dusting) look at it from all angles, and make sure there are no low spots\high spots (this step is optional, but it helps you to see if everything is sanded well)
spray the entire box with a coat of the high-build primer, and wait till dry. proceed to WETSAND the primer with some really high-grit wet sandable paper (using water while you sand acts as a lubricant and smooths it out quite nice)
i would prolly do this one more time.
then do the exact same procedure with your paint, you better be sure that your box is smoother than your ***, cuz after the paint, you will see if it is or not.
the last coat - wetsand with the HIGHEST GRIT paper you got.
now do a clearcoat or 2 with the wetsanding in between.
SEM is a good brand of paint and clearcolor. ive been recommended by
tim at hzemall (the guy who does the installs) to paint with this brand.
ive read numerous articles on painting, but i have yet to do it. if anyone feels that there is a step im missing, feel free to correct me.
and your all done. painting a good paintjob is ALOT of work, this is why painting cars cost so much money if you get it done right.