Hi,
You may wish to read Jerry's posts in regards to the alu sandwich mounting of PVC blades. I am using it to make sure my blades to not fly off in strong winds. The sandwich consists of two alu pieces (curved) and attached to bolts one inch or more in from the PVC edge. The bar or bars to the hub get connected at the edge. Yours should perhaps be a bit longer.
Connecting at the edge probably means a larger angle of pitch which helps starting up in lower winds but does not help in stronger winds.
Regards,