If you are going to do any fiberglassing, it will help tremendously to have some fiberglass rings.

The pics above show a MDF ring for a 6.5" speaker. We countersunk it with 1/2" MDF and also put an inside diameter chamfer and rabbited the outter diameter as a groove for the fleece to be stapled to before coating with fiberglass resin.

I can make these for you! This ad is for a pair of rings. Please let me know the cutout diameter of your speaker, the outer diameter, and I can make some similar rings for your project. 

You may choose to have them just straight or I can put the camfer or rabbit bit on them as well. Let's talk. Let me know what I can build for your DIY project today.

Thank you!