Go get some astroturf. It's made to be outside so it won't get musty.

heat is no issue i live well lets just say where the coldest it will get when i hunt is 20 degrees i put it in there to help protect the plywood and to keep noises lower...our season starts the 16 of october

Just watch out for frozen carpet!! I've been there before. You would be way ahead to replace your bottom with steel mesh if you can find some. Probably any tool & die or metal shop would have some.

where ya ta, ill mail ya a new piece

I built a box blind to hunt over an ox-bow in a creek. It's up on a hill. If I had put a ladder stand there I would have been above the tree canopy on the other side of the creek. I put astroturf inside the box to keep the noise down. It shouldn't get wet in there, but if it does, it won't mildew.