Yes there is a small space at the top edge of the tub. It is small enough that the snake cannot squeeze out, and just big enough to allow the tub to slide in and out easily. There are a couple I got a little too tight, and they rub just a small amount. But they work fine.
I used a drill to make the holes in the tub, and yep I cracked a couple. But the cracks are pretty small, so no big deal. Doesnt hurt the containers any.
To heat the rack, I used peg board for the backing and attached heat tape to it. I got the heat tape from The Bean Farm. I used the 11" flexwatt heat tape and the electrical connectors from them as well. I wired the heat tape through a rheostat light dimmer switch from Lowes that was rated at the flexwatt heat tape maximum wattage. I mounted the switch on the side of the rack using a common plastic double light switch/plug housing. I hooked the rheostat switch up to an electrical plug unit and put it in the same housing. This way, if I ever need to replace the heat tape or I need it for something else, I can just unplug the heat tape and take it off. If you want I can take a pic of it and post it for you.
Brian
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1.0 Corn snake
1.0 Black rat snake
1.0 Albino Black rat snake
1.0 Everglades rat snake
0.1 Yellow rat snake
1.1 California king snake
1.0 Prairie king snake
0.1 Black king snake
Good luck and Happy Herping
Brian