So I'm building a rear seat subbox since no one can fit back there anyways. I removed everything tapped it all off, tapped on a layer of duct tape and its ready for its first layer of fiberglass. I have done a little fiberglass work before but I'm not sure if what I had in mind will work. I may need to fiberglass all sides of the box without mdf. Has anyone done this and has it worked? Anyone in the area with good fiberglassing experience can lend a hand?

having an mdf frame or at least some mdf gives a lot of rigidity. without any i would look to do many layers of fg mat to give it the strength necessary. what i've heard is if you can press on it with your thumb and it flexes at all keep adding layers of mat and resin.

will fiberglass and resin stick to mdf? I was thinking of getting the mold from the gap where the seats have been removed by fiberglass then using mdf for the top and the side facing the front seats. How do I get the mdf to bond with the fiberglass mold that I will make in step one?

yes the resin will stick to the mdf. i've used candle wax overtop the mdf along with mold release to help pull the fiberglass part off. worked really well. The last thing i made out of fiberglass, i used cardboard and put masking tape overtop along with mold release and it worked perfectly.