I'm following your thread, great stuff,thanks very interesting.
Im approaching this more with thoughts of simply spreading tie out loading (on larger panels than ive seen anyone mention) rather than adding diagonals to also increase material strength in lighter applications.
I had envisaged (even free running) lines through the perimeter hem simply spreading the load much like an extension of the warbonnet corner. ie Im wondering whether bonding the hem reinforcement (at all) makes any difference when it is in tension. With nothing moving once the tension is in place wouldnt this eliminate the need to get your (bonded in) hem reinforcement under even tensions and pressures before bonding and the need to get the bond consistent along its length so that pressures dont vary on the reinforcement if the bonding itself isnt entirely consistent.. perhaps a simpler approach in which the reinforcement material (ie cord (or tow) resistance, bonding ability) isnt so crucial and can be chosen for durability/uv resistance instead.
hmmm... simple thoughts though difficult to explain perhaps?
I like the approach you are using. It will be interesting to see how you finish the corner ties and how you incorporate the diagonals. I imagine that you will need to have a design which allows tensions to equalize or very accurate even tensions when the corners are finished / reinforcements joined (even if incrporating your reinforcement with the tarp fabric itself..)
All the best!