heres something i wrote on a different forum
im not sure what ur ideals are for a box but buy some tinfoil and duct tape to put down wherever u need to make a mold so it wont stick to ur truck
tinfoil/duct tape getting layed down
layer of glass, i normally do 2 layers of glass while its in the car/truck then i pop them out and add more layers in the garage or whereever it is that ur working
i didnt do anything special with this box as i jsut wanted somehtign quick and ended up with this
and heres some pics with the MDF rings and dowels
first setup ur frame, i used 3?4" MDF and 1/4" dowels and hot glued them togehter
streched a old shirt over top and pulled it TIGHT and glued all the edges...some people use a staple gun
put a layer of just resin on the shirt or whatever u use, and make sure u put alot on so it soaks thru the entire thing
let it dry and then scuff up and add several layers of glass
for some reason i didnt take any pics with hte glass on, but once its nice and thick cut out ur hole and do a thin layer of bondo to smooth things out
forgot to mention theres no point in wasting resin/fibreglass in the sub opneing but make sure u put it on good where the shirt meets the MDF rings for ur speakers as u want to make sure it stick tothe wood good
i ahve more fibreglassing pics if u want some more
and check out this guys work on his Z24, he doesnt really go into much detail but just looking at teh pics helps alot
http://www.v6z24.com/jbodyforum/viewtopic.php?t=83376