hahah thanks. You can definitely do it, I had never used fiberglass or done anything like this. Just had to redo the driver side one 3 times before I was happy. Its actually very inexpensive so I didnt mind starting over. I dont have any pics as they were being built but I can try to give you some steps and hints and if you have questions along the way you an always reach out to me.
1) Used cardboard to make a template and then transfer over to 3'4" MDF. You may want to use 1"2 or something smaller depending on what seals you have. Mine are the civic 2 door which are thicker on the inside but ended up making a super smooth transition with the box.
2) Once you have the shape in MDF, I used a router table (cheap ryobi) to chamfer the back side edges all the way around and I also rounded over the top edges. I dont think this is totally necessary but I do think it helped the transition where it meets the seals. I also cut a 5 or 6" circle where I think my speaker will end up being so I run the wire through and it also gives me a little more room so the speaker doesnt hit the MDF when mounted.
3) Now that you base is complete you need to make speaker rings. There is a number of ways to do this but I bought a circle jig from amazon. For the 6.5" speaker I ended up gluing 2, 3/4" (thick) circles together to get the speaker to drop down and be recessed. This worked out well and just a little bit of the grille sticks out. I didnt cut 2 circles for the tweeter since it sits in a flush mount cup and doesnt stick out far.
4) Once you have the circles cut, test fit your speakers to make sure they will fit with the grille and entire assembly! Then you can use shoe moulding, doll rod, whatever you want to create stand offs or legs for the speaker rings. You can cut them whatever length you want and angle the rings anyway you like. I hot glue mine in place then go back with silicone so they never fall out. Its a little bit of a PITA to hold the rings and try to glue a leg or two at a time but its doable. Try to mount your tweeter and speaker relatively the same height, it will be easier to wrap in the end.
5) After your rings are in place test fit the speakers again to make sure they dont bottom out on the MDF and you like the angles that they are pointing at.
6) Get cheap polyester fiber from Joannes or your local craft store. Youll want to stretch this overtop of your piece and staple it to the backside. Do one edge at a time, pulling wrinkles out. The poly is stretchy and thats the key that will allow you to have no wrinkles.
7) Once thats complete, youre ready to fiberglass resin the poly. I think I used about 80 ounces on the first round. Mix smaller batches though. I think I did 2, 40oz batches. You want to completely soak the poly so that it turns dark. When you think you have soaked it, put some more on
Let dry and you now have the shell. Oh, I dont resin the speaker holes since you cut those out anyway.
8) I never used any actually fiberglass mat or cloth and I'm not worried at all about strength. After that I used a thin layer of bondo to get a smooth surface and contour anything I needed to. Sand down once youre happy. I also used an angle grinder with a flap disc to grind the backside down smooth and flush. You dont need the staples or that extra material anymore.
9) Youre ready to wrap in whatever material you want. Again, try to pick something with some stretch so you can pull wrinkles out as you go. For this, I used spray glue little but little and then pulled hard to get the wrinkles out and stapled to the back. Corners are kind of tricky but they will fold over behind the MDF and be fine. Cut away excess material so it doesnt build up and push out the kick panel.
10) install and enjoy?
In before TLDR haha. MSG me and we can chat if you have questions or need more info!