The bikes come with 2 holes on either side of the bike - near the derailleur and disc brake - to mount the rack supports. For the park guys, I drilled 2 holes near the seat and installed rivnuts onto which the rack attaches. It pretty-much just works. I'll try and post some pictures soon.
Yes..or something like this http://www.ucycle.com/product/jandd-rubberized-p-clamp-4604.htm
For the large triangular shape of that part of the Juggernaut frame, it would likely need to be the large size.
At my local bike shop, I bought both a seat collar and a pair of these P-clamps and will try both and keep what works best.