I've wondered this as well with the camper shells when reading posts about making them from scratch thinking it would be much easier to start with a shell and cut it down.
Fiberglass is not very hard to work with. Get good epoxy and measuring cups. I like West Systems because they have pumps that connect to epoxy and hardener cans and dispense the amount needed from each (4 to 1 I think). When laying down new glass mat, put down layer of epoxy first and then lay the mat from 1 end to the other to avoid bubbles (like you would with an ecomodder sticker
) Custom sub enclosures are usually done using pantyhose stretched around the framing I think. Also make sure to stock up on cheap brushes since you'll ruin many of them.
MAKE SURE TO WEAR A DUST MASK WHEN CUTTING THE FIBERGLASS!!!! A respirator with the filters would be better than just a mask, but at least the mask is some protection.
Would also be smart to wear something with sleeves as fiberglass dust is very annoyingly itchy and doesn't always come off in the shower. Also remember the dust all over your clothes when you are done as you and your family are at highest risk of breathing it in while inside the house...and you are most when removing your clothes...non-pullover shirt would be best...
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-Mike
2007 Ford Focus ZX5 - 91k - SGII, pending upper and lower grill bocks - auto trans
1987 Monte Carlo SS - 5.3/4L80E swap - 13.67 @ 106
2007 Ford Focus Estate - 230k - 33mpg - Retired 4/2018
1995 Saturn SL2 - 256K miles - 44mpg - Retired 9/2014
Cost to Operate Spreadsheet for "The New Focus"