Re: Custom seat pan
Bones, there is a foam that they call 'motorcycle foam'. It is very high density foam and a 2" pad will be sufficient for a saddle. I know there are grades of foam rubber designated by numbers but I don't know what motorcycle foam equates to but it is firm.
I've used it for several saddles and it will absorb the bumps and protect my bony little rear just fine.
Check with your foam supplier to see what they recommend for the firmest foam rubber available. The thinner the saddle the better it will look on your seat design.
Good luck and show us the finished product.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"