If you're going to carry gear at the higher end of the comfort range for the Crown VC (let's say around 30 lbs), does it make sense to look for a different, stiffer framesheet? Or perhaps add another sheet to the first (there's plenty of room in the framesheet pocket)?
If yes, where might one find a stiffer framesheet? I noticed on the Nimbus Trace, they're now using maple wood (!) as the framesheet. Makes me wonder if 1/8" plywood would work.
I have a kneel pad made of blue CC foam. Trimmed it to fit into the Crown's framesheet pocket, would that increase stiffness and thus carrying capacity? Or would it just pad my back a bit more?
In which dimension is the stiffness important? Do you want the sheet stiff top-to-bottom, a vertical stiffness that resists folding/collapsing from top to bottom? (If so, the existing Crown VC sheet is not very stiff in this dimension). Or is the stiffness important in the horizontal dimension, ie, that it resists conforming to your back? Based on all the aluminum-stay type frames you see, I'm guessing you want little flexibility in the vertical dimension (so the top of the pack does not fold/sag down) but you DO want flexibility in the horizontal dimension (so the frame moves with your back).
If the vertical stiffness is the important one, than simply adding one or two flat aluminum stays, oriented vertically, to the existing framesheet, might stiffen the Crown VC for heavier loads.