check out www.paysonoutfitters.com
they carry a complete line of eberlystock packs at slightly better prices and offer free shipping.
they also carry other brands.
i bought an x1 from them and it is indeed an excellant pack. not what you need however.
i would think there are other more reasonable options for your intended use.
a g i duffel bag holds lots of gear. possibly something on that order could be fastened to a good frame.