Fiberglass advice....

so I am finally going to start on my first fiverglass job. It will be to put my 5.25" midrange in the kick, and probably the tweet too.

What I was thinking, tell me if this would be a good idea or not, was find a junk yard and get a second set of kickpanels for my car and just add on to them, that way they snap right into place if that makes any sense at all.

any suggestions or advice at all is great.