I've more or less cemented all the major design features in my mind, and I've ordered all the hardware, webbing, and shock cord. I was really pleased with how inexpensive it all was. I'll be using free 'fabric' (feed bags - it is a prototype after all). The foam I'm using for padding was left over from another project, so it's essentially free. I'll also be using a nice piece of birch plywood that a friend is going to give me for $3 as a frame sheet. With all that and the thread it'll take, I estimate this project will cost about $13 and some time.

Here's a few details about the design, though it's still somewhat fluid.
* I'll be using a full wrap-around style hip belt with generous foam and 1 1/2" webbing. It'll slide into a sleeve on the main body of the pack, so it'll be removable. If everything works out, I'll strongly consider adding pockets to the hip-belt.
* The shoulder straps (SS) and load-lifters (LL) will be the McHale style where the LL and SS adjustments are independent.
* I'm considering steaming and shaping the plywood frame sheet into a more natural curve, but I'm not sure. I've never tried to re-shape plywood, and even if it worked, it might not be worth it, especially with a wrap-around hip belt holding it off of my back anyway. I will probably also drill holes in it to lighten it up.
* The main body of the pack will essentially just be a minimally modified feed bag, but I will rip the bottom seam and add a better shaped bottom so it's not flattened out like an envelope.
* The top closure will be the dry-bag style where it just folds down a few time or more and then the two side clips buckle to each other. Or, would that be, "the two side buckles clip to each other"?
* Even though It'll have a frame sheet, I'll still put my pad in it to take up extra volume and stiffen it up. Hopefully, this way, I won't need compression straps. If this doesn't work, I'll add compression straps by hand down the road, or I'll just know I need them on my 'forever-pack'.
* The feed bag material is very water-resistant, if not water-proof. I might seal the seams.
* I'll also do the more or less now-standard large exterior pocket to hold wet or quickly-needed items and two side pockets for beverages, all with shock cord at the top. I'll also punch drain holes in the bottoms of the pockets.

Can you tell I'm getting excited?