After many outings I've come to the conclusion that my loadout is just about perfect but I'm not in love with my pack, a 32L Osprey that's just a bit small for my cold-weather insulation).  Good excuse to make something that's exactly what I want & learn a thing or two.

I've made my hammock & quilts, rainfly, and some other odds & ends, so I think I'm ready to do a bespoke rucksack.  There are a few sites & posts scattered around that discuss construction of setups vaguely similar to what I have planned, but others seem to be behind paywalls (namely BackpackingLight).  Are any sites in particular worth looking into, or is this a question best left to the Hive?

The premise is a long, skinny oxygen-cylinder-shaped pack body full of the stuff I always have and that must stay dry (insulation quilts, bear canister, spare clothing), forming the structure that the remaining stuff hangs off of on webbing.  At least on paper, I get a better weight distribution and organization than the larger rectangular packs you usually see.

-A 35L-40L total volume range at the end of the day as-configured, hopefully about 2-3lb empty and capable of holding a 40lb load (usually more like 35lb, though)
-Tubular main body with roll top (too many zippers have failed on me) and two circumferential compression straps, about 9"diameter x 36"length
-Waterproof (basically a big dry-bag) and moderately abrasion-resistant
-Three runs of PALS-type webbing down each side (one of which is structural & carries the roll-top cinch load)
-A run or two of webbing down the spine that attaches to the frame (not sure on the details yet)
-A bent fiberglass rod inside a teardrop-shaped web of taut fabric is the frame & back pad, a run of webbing down the spine attaches to the pack body somehow
-The ends of the frame rod stick into stiff sewn sockets at the rear of the waist band/pad to carry the weight of the pack
-The pack is stabilized against side/side rocking with a pair of straps between the pack body & waist, and the pack body & shoulder straps at the frame
-Two large hydration bladder or water bottle pockets attached midway on either side, sort of acting like kidney pads (at least when full)
-A smaller pocket above & below the bladders on each side for smaller items (four total); hammock, filter, rain gear, and electronics/first aid

I have absolutely nothing to offer as far as building the pack, but 36” long? That thing will go from your waist to past the top of your head.

Yeah, it'll extend from just below my tailbone to right behind my head.  Also, remember that it'll be roughly spherical on the ends and that length is tip to tip.  Almost just like a large SCUBA tank, lol.  I plan to have about 1.5" of padding offset between my waist and the actual pack body, so the bit that hangs down won't be dragging on my rump or anything like that.