1. Round all 90 degree angles either by sanding or using BONDO and sanding them round/smooth. Especially back corners in the box.
2. When bracing the walls of your enclosure inside of the box, use threaded rod rather than wood as this reduces turbulence and takes up less airspace.
3. Use ¾inch MDF or thicker on the entire enclosure.
4. Make your baffle double thick so that the front doesnt flex.
5. Make sure to use wood glue on all joints of the enclosure when putting the pieces together.
6. Use liquid nails inside of the enclosure on all joints once the enclosure is glued and screwed together.
7. Once all changes are complete with port tuning, secure the port with plenty of screws, wood glue and liquid nails.
8. Round inside and outside of port ends to reduce turbulence.
9. Once the enclosure is tuned and all changes are complete, coat the entire enclosure with fiberglass resin. It may take 2 coats because MDF is very porous.