"moldless" fiberglass/cf construction? Options

[obaa996]

With all the expertise on this list, I thought this might be a good place to start....
I'd like to build a new backpad for my car; I have aftermarket seats, so the stock pad doesn't fit, and besides, I'd like to embed a subwoofer box into it anyway. Since this is going to be a one-off, I don't really want to go through the effort of building a mold, etc. for it either. What I'd like to do is build some sort of form (in the car) which looks like what I want. Hopefully, II can then cover it with fiberglass to form the basic backpad, and then cover it with a layer of carbon fiber (because I like the way it looks). When it's all cured, I'd then remove it from the car, remove the form from behind, and then add more fiberglass to build up the box.
It all sounds good just talking about, but how hard would it be to actually do? What can I make the original form out of? How do I seal/finish off the foam so I can lay fiberglass over it (and be able to remove it later). And how do I get the different fiberglass/cf layers smooth enough so that the finished product will be nice appearance-wise?
All the sites I've found online all discuss building a mold first, but I can't imagine that all the custom pieces I've seen at shows, etc. resulted from a plug/mold/finished part process just for a one-off piece.... Any suggestions here would be appreciated!

[URY914]

I agree with both of these methods, BUT if you've never done any f/g work, you are in for a lot of work. And your work is going to hidden it behind the seats.
I not trying to change your mind, just warning you.

Good luck.
Paul