I have been planning the exact same thing, I was thinking of using a zipper, but then I would have to custom order one that size. I too was worried about it tearing, but I think Slowhike is right. You should be ok as long as you reinforce it
Psalm 19:1-3 "The heavens declare the glory of God; and the firmament sheweth his handywork. Day unto day uttereth speech, and night unto night sheweth knowledge. There is no speech nor language, where their voice is not heard."