Fermentation Chamber Question

I am converting the spare fridge in my garage into a fermentation chamber so I can control temps better. It's hot here in South Carolina!! Any suggestions as to what I could use as a base to rest the glass carboys on, while inside the fridge? Plexiglass? Lumber?? I am not 100% convinced that the existing "shelf" will support 40+lbs! Not a chance I want to risk it. Nuh-uh.
What's everyone think?
Thanks!

Wooden shelf would work fine. Sometimes all you need is a vertical brace to help the existing shelf if it is spaced right.

I ripped out all the original shelving and built a wooden shelf to fit as close to the bottom as possible. Here's my build:
https://www.homebrewtalk.com/f51/my-kega-fermerator-build-123889/

I just added a 1/2" piece of plywood cut to fit.

I am going to be diving into a small project of this sort here soon and I have a question:

Taken there is a standard sized fridge- how many carboys can you place in the fridge at one time?

I pulled the shelving out of the door, which increased the fridge depth by 3-4 inches. You'd have to measure the refrigerator. I can fit 4 fermenters (carboys/ale pails) in mine at one time. There is another thread around here somewhere with a side-by-side refrigerator converted over, and I think he said he can fit 5-6 carboys. If the inner dimension of the refrigerator is on the order of 30 inches, you can probably fit 3-4 carboys inside it if you pull out the original shelving.