Alt Bike Culture - making my own seat pan (questions)

what kind of metal should i use for the pan, including thickness of the metal itself? i'm looking to build a single long seat for a tandem frame (see my other post). also, does anyone know how i would go about making decently strong seat rails? i'm pretty sure i can figure out the foam part.

Probably a light guage steel. I'm not professing to be a metalsmith so I have no idea of a GA number. Just take a hammer and beat the crap out of it until it looks like a seat pan, cut off the stuff that dosen't and reinforce it.

Probably easier would be to to buy two similar banana seats, cut one in two near the mid point and cut the ends off the other, then spot the three pieces together doing a litle hammer & dolly work as you go then stitch it all together.I'd probably feel good about putting some channel stock on the underside to reinforce everything to reinforce the longer clearspan.

if its a seat pan for a bicycle you could go with something pretty thin, as the seat width will also be thin. 12-14 ga sheet would be more than enough.

Here's a photo, without padding :
http://i134.photobucket.com/albums/q119/hotbike/Type9inthepark.jpg
the seat pan is slightly concave.

I use 7 layers of fiberglass when making a seat pan. (About 3/16ths of an inch).

There are no seat rails, it's ALL fiberglass.

^^^ how sturdy is that? im not as familiar with fiberglass as i am with metal...

How sturdy? Fiberglass is as strong as steel.
Here's a picture with a half inch of latex foam over the seat pan:
http://i134.photobucket.com/albums/q119/hotbike/Type9Pink2.jpg
You might not be able to tell the seat-pan is concave with the padding on it.
The rest of the bike is quarter inch thick fiberglass, except the top of the fairing, which like the seat is three sixteenths of an inch thick.
I sold this bike for twelve hundred dollars and I'm testing another. The new one is a BMX with a banana seat (no picture available), but it has a Suzuki fairing, not a homemade fairing.
I was able to make an impression of my arse by sitting in a pan of joint compound, with a layer of saran-wrap on top, so it didn't stick.
Although it has worked for me, I must say that the underlying support structure is holding most of my weight (I weigh 250 something), and the seat pan is bedded in silicone caulk. I don't know if it would work with traditional seat rails. (with a seat post).
This bike used up eighty yards of four inch wide fiberglass tape and almost two gallons of resin.
Sorry I didn't reply sooner, the bike forums server is very slow on some days.