I have a Camelbak "Commander" 2,800 cu. in. hunting pack that I also use for backcountry skiing due to its features, several of which are my own mods.
This pack came with a cloth "waistbelt" and a plastic framesheet. Both were useless for transferring loads to my hips.
1. Removed the cloth waistbelt and put an REI Ridgeline padded hipbelt which I slid in behind the pack's lumbar pad. Fits like it was made for it.
2. Left the framesheet in and bolted on an upsidedown "U" shaped aluminum frame I made from 1" wide barstock. The frame resides in the zippered hydration bladder compartment but bolts thru the plastic framsheet. I pre-curved the vertical stays to fit my back.
3. Did a few other mods like sewing on 1/2" webbing and QR buckles to the pack bottom to hold a mattress, etc.
4. Added aftermarket zippered side pockets for more volume. They are held on by the two original QR buckled compression straps on each side so are easily removable.
And yes, it is more "comfortable" than it was by a quantum amount. Now I can carry 45 – 50 lb. loads (if I have to) in RELATIVE comfort.