Frame for rear deck lid

I don't know if this has been covered but I've built a frame for my rear deck out of 1x12 so I could get the radius of the rear deck and it broke 5" from the hinge on both sides. So I'm wondering how to make my frame so it doesn't break and having almost no budget to work with I'm thinking I should go with 3/4" plywood
any suggestions would be appreciated.
