They've been made. I think they were moderately successful, but nothing real big.
I know. One certain maker goes all out describing their 'super awesome' special UV protectant material. Guess what folks - it's outdoor patio furniture fabric. Nothing super secret about it. They were charging like $200+ for this 'special' cover.
In reality, the material cost would be considerable - about $60. We were hoping to make them in the $100-$150 range.