Its gonna be about 5 gallons. There's gonna be an airtank mounted on either side of the framerail behind the tires. I posted a pic showing a similar setup a few posts before.
Heres a quick update, Finally found a job so I can has money! Gonna try and finish up the airtank/crossmember and get it welded in. Once thats done its time for some bent tubing on the backhalf!
Thanks guys. Been messing around with the frame model trying to see what I wanna do with the tubes for the back. Heres a quick pic, its not done and not exactly the same but you get the idea. The blue bars are going to tie into the upper bag mounts.