Is this for a hot herp? I did this for one of my 55 gal and it worked great I did have a few differences though.
I use one peice of plywood then cut the doors out of that, then used sach locks on the doors, I drilled a small hole in the curved part of the sash lock to put a small pad lock to keep it locked. It worked good. The reason I went with one piece of wood is because the center divivder on my 55 would bow in or out and I didn't trust it.
Yours looks great and I can't wait to see it finished, the only thing I would do is to check or re-silicone the plastic tank top just in case. You never know if a snake can pop that top right off! I kept an adult male TX rat in mine for a month to test it lid and that was the only way he got out.. Rock on, Blue