mrdon, funny that you should ask.....the gas tank was one of the hardest parts. I tried a few designs before getting this one working. Size wise I would make it as big as possible but remember chain clearance and to pitch it so it all drans to the pump.
My motor is fuel injected, so on the bike the fuel pump sits inside the tank. I made all of the tank out of 1/8 aluminum, except the bottom center section...its 1" thick aluminum. My fuel pump fits as it does in the stock gas tank...it fits up in the tank from the bottom. I used the 1" for the bottom so i could drill the holes and tap them for the pump flange. The gas cap is at the highest point in the tank (might seem common sence, but this is VERY important). For the cap i used a non-vented cap from the duce factory but drilled two tiny holes (1/64th or so bit) and used the guts from a brigs and stratton gas cap underneath to work the vent, it worked out perfectly.
That gas tank as one of the most time consuming part of building the bike. I still wish I would have made it bigger for longer trips down in daytona.....so I proboly will re-do it sometime.
--John
this is little off the subjest but love the banshee, i'm in the process of doing the same thing but with an R6, how did you do the gas tank. Hope you can fix the Spyder problem so it will be alot funnier to ride then.