Thanks Smulkin, the main purpose of the wedges and cardboard on the sides that you can't see is to keep the tubs tight to the shelf above it and also to kee p them off the heat pads I'm using temporarily. The 3 tubs with the spacers house some of the newest snakes I have in: a pair of het albino boas and male het albino ball (by next week a het female ball also)...they are all this year's and small so I didn't want any chance of escape. There is about a 1/8" or so gap between the tub and the and shelf above it on most of the tubs..depending on if the floor is bowed or not forcing it up a little higher. My plan is try heating from the back with with the flexwatt and making adjustments as I go such as adding the ply side panels. There ended up being a perfect space at the back of each shelf where I can lay the heat tape and it won't be touching the tubs, the more I think about it though I probably will need the sides so the heat dissipates towards the front rather than out to the near open sides of the rack.

suggests and comments welcome for sure!

Heath