None. I never used or owned a UV unit.What type of UV sterilizer are you using on your tank?
I glued and toe-nailed the vertical 2x4's and glued and straight nailed the horizontal 2x4's. It's more than strong enough. There is no lateral movement at all.How did you attach the horizontal 2x4s (along the top and bottom front and top and bottom side) to the vertical 2x4s?
I used tongue and groove knotty pine boards, glued them together and screwed 2 1x2 strips to the back to stabalize them. They were very easy to build.Also, on your doors, are those pre-made or did you glue them together with rabbits and then plane them?