I have an update!! This really was a ton of work, even if it doesn't look like it.
As I said earlier, the biggest piece of plywood I can put in my car is 48x30, with that I need to duck when I'm driving, if I go with 48x24 I can use the passthrough and it's more comfortable. So I needed to get a little creative with the back panel. I think I ended up with a nicer look in the end, and it's super light, I decided to glue it up like the worlds largest shaker style door.
This was a test fit with one panel, where you can see the routing that it drops into, and the counter routed styles for strength.
Comet inspecting my work:
This is the panel glue-up. Once again, the size is the biggest challenge here. This panel is bigger than any work table I have so my only choice was to use the hardwood floor. If you choose to copy my method I have two tips:
1. Make sure to get divorced first.
2. Wax paper is the best thing to use to protect the floor. The glue doesn't really stick to it.
Finally, and this step was finished only a few minutes ago,... I have the holes for light wires, pump wires, and the two fans routed out, the pocket holes drilled, and the glue attaching it to the main box is drying now.
Comet seems proud of me:
Whiskey