Re: fiberglass or steel?
"Make a form out of cardboard or foam, lay on your glass fabric then slather on some resin." Not so sure about this one unless you're using epoxy resin. Polyester resins will melt your foam right away. Epoxy would be a better choice anyhow as it's technically an adhesive. More expensive but resists the elements way better and stays a bit flexible. I built an epoxy over foam over steel frame utility trailer over 20 years ago and it still looks very nice (think rolling ice box). Painted it with a 3 part acrylic. The lighter mats and cloths (6oz.) conform nicely to irregular shapes as well. Also no visible rivets or screws anywhere on mine. Remember this stuff heats up when catalyzing and thins out just before setting so if on vertical surfaces, a dry wet out (on a table) transfer onto the surface is your friend. Spent almost 25 years in the marine repair business (engines and fiberglass).
I am an sojourner in the earth; hide not Your Commandments from me. Psalm 119:19
Here is the patience of the saints; here are the ones keeping the commandments of YAHWEH, and the faith of Yahshua. Rev. 14:12