Not about the custom dash part per se, but while you have everything out, take the time to throw a couple Bulk Pac's of Dynamat Extreme or similar resonation dampening mats on every flat surface. It isn't so good at keeping heat out, but it is great at reducing noise and panel resonnation. And, once the interior is back in, you can't tell it's there.
Then use the double-sided foil covered jute mats to cover the entire interior from headliner, under door panels and on the floor from the bottom of the front windshield to the bottom of your rear glass. I used that peelable wax-paper covered aluminum duct tape to seal all the seams (and there were a lot) AND the edges of the foil mat to the car body.
Once I had it all fitted and covering the entire surface form end-to-end, it looked like a tailor had pieced together probably 45 separate panels including some larger ones to tightly fit it into a continuous covering. I could remove and replace the finished panels that retained the shape of the floor etc. I then taped down the edges to keep it in place.
On my hardtop, it sounded like you were in a vault when you closed the doors after. The road noise was quieter than being in a Bentley when going down the road after that, and the A/C was dramatically more effective. It was also a great vapor and heat barrier. Well worth the time. on a hardtop.
For the double foil covered jute, the best deal I found on it so far is from Speedway motors. For the Dynamat Extreme, I just searched for free shipping and the lowest price on-line, because the stuff is heavy.
On a side note, you don't have to cover an entire panel with Dynamat, rather use it in strips to deaden the panel's resonnation, because the real heat, noise and vapor barrier is the double sided foil mat. I learned this from an article on how to best insulate a small airplane without adding excess weight.
