Box / Enclosure Idea - Will This Work? Dallas box builder?

[Captain Awesome]

I want to add a little bottom end to my sound system. I am probably going with a single sundown sd-2, either an 8-inch or 10-inch, depending on the volume of the box.

The thought is to have a custom box built, probably out of fiberglass, that will fit perfectly into the driver's side well of the plastic tub under the back seat so that it doesn't move around or rattle, but it is still removable whenever I need the space for something else. I guess the speaker terminals would have to be on the face / top of the enclosure.

Does this sound reasonable or doable?
What should I expect to pay for this enclosure?
Any suggestions for someone in the Dallas (TX) area to build this for me that won't take advantage of me?

Attached are photos of the location.