Does anyone know where to find the dimensions for the front trunk removable panel that goes over the spare tire? My car didn't come with one so I was going to DIY one. How did the factory install it, like is it supposed to just sit on the tire?

Yeah, it's nothing special. Just measure the width and length of the compartment, leave about 1/4 - 1/2 inch space around the edges, and cut it out of some 1/4 inch plywood. The front edge is rounded to follow the curved body panel, and they do just rest over the spare tire.

A bit of black paint and some carpeting and you'll be all set. I believe that you can get the proper carpeting at Auto's International or any of the other upholstery shops that provide upholstery kits.