Yes, more info please! We've talked about magnets before, but---as far as I can recall---you're the first to go so far as getting rare earth magnets and actually doing it.
You could make different "under-hammocks" ("magna-hammocks??!?!?") for different applications. You could make one out of organza for an ultra-lite under quilt hugger. Or one out of sil-nylon as a lighter weather shield than your PU coated one.