How to put a shelf that will hold a 40 breeder?

Okay my 55 has.an empty space in the stand want to but a shelf inbetween to hold a 40 breeder but wat will hold it in place without it stressing and end up falling apart.

Take a pic.

I will wen I come home from oklahoma, it has four sides lol. its open in the back and front. Ill be putting a back the front will have the plastic doors I will be making.

Ok forgive the dumb question. Is the breeder going to hang out the back of the stand?

It depends if the filter does, I dont have the tanks yet but I was wondering how to doit.

well... consider this.

standard 55 dimensions 48x13x21

standard 40 breeder 36x18x16

So the 40 is 6 inches wider than the 55. you'll need to take this into account if your stand is only 13 inches deep.

Hm... Ill measure the stand to see how wide it is. I know its long enough and deep enough but width maybe a problem. I might be able to add a few more inches or build a stand that will hold 2 40 breeder and shove it in the closet.