Don't use foil tape on the flex watt. Regular electrical tape works just fine. Personally I don't hot glue my probe to the flex watt.
My racks uses 32 qt IRIS Sweater Boxes, and I have no trouble fitting two medium RBI hides and a 4 inch ceramic water bowl.
They don't need a ton of room to roam, and mine will cruise on top of the hides at times. The tops of the hides are flat, so it's like having elevated floor space.