What type of backing should I put on my melamine rack system?

I have recently created a melamine snake rack. I only created the sides and slots, not the backing. I was trying to only use one sheet of melamine. I am going to be doing back heat and not under heat. This is not the discussion point of the post. I was wondering what I can use for the backing since I am going to have heat tape directly on the backing. Would it be okay to buy a thin piece of plywood and coat it in foil tape or would it be easier to simply cut another piece of melamine to cover the back? I would link a picture but imgur is not working. The dimensions are "25.25in x 48in"

Either plywood or melamine would work for back heat. I would go with thicker plywood over thinner to help insulate the back of the rack and minimize heat loss if the rack is to be used in a cool area.

I used 1/8" panel board for backing on both of the racks I built. It's cheap, easy to work with and it's laminated, so it's water resistant. I think it's only about $12.00 per sheet at Lowes...