pcmofo

Nice project!

It is very common to mix MDF and fiberglass as needed. The only reason to use fiberglass is to build enclosures in spaces that are not flat. If you want any part of the box to be flat MDF is cheaper and easier. You can still use it for the rear and sides etc. The difficult part with your design would be attaching the fiberglass shell to the flat MDF. I would follow the instructions and make the shell, trim the edges etc then use the epoxy to glue on MDF to make an internal frame 1-2" thick. You can reinforce the MDF to fiberglass joint with additional layers of fiberglass. Then make a MDF front baffle and screw/bolt it into the MDF edge with nice screws or bolts and T-nuts. You can use glue/calk and make this permanent or use a foam/weather sealing gasket and make the front removab...

It is very common to mix MDF and fiberglass as needed. The only reason to use fiberglass is to build enclosures in spaces that are not flat. If you want any part of the box to be flat MDF is cheaper and easier. You can still use it for the rear and sides etc. The difficult part with your design would be attaching the fiberglass shell to the flat MDF. I would follow the instructions and make the shell, trim the edges etc then use the epoxy to glue on MDF to make an internal frame 1-2" thick. You can reinforce the MDF to fiberglass joint with additional layers of fiberglass. Then make a MDF front baffle and screw/bolt it into the MDF edge with nice screws or bolts and T-nuts. You can use glue/calk and make this permanent or use a foam/weather sealing gasket and make the front removable.Another option would be to stretch the fabric and mount the trim ring in such a way that the box appeared flat though MDF is way cheeper than fiberglass to cover that area.