Yes, there is a spot routed out for a thermostat probe, so you can stack them and have the flexwatt in between. I personally like their heat coild method too, but that deffinitely has to be on a thermostat. It is not quite as even, but convenient for moving since it is set in well.
Any floor heat is not going to bring the ambient temp up "too" much, but that can be a good thing. AP cages are amazing at holding temps and humidity, so you will get a great gradient with a room temp of 73 and 11" heat tape.
I would do an 11' strip of heat tape on one side of the cage that runs the depth of the cage (2ft).
Only problem with cleaning is the cracks. You arent used to them because visions are injection molding, while AP are CNCed sheets. I personally don't seal them anymore because it comes off too easily and is more pain than its worth. They minimal difficulty with the cracks I honestly don't have a problem with, and I have only seen a TINY amount of liquid ever make it through them even when they arents sealed. I keep all tropical snakes on a misting system, and I would be pissed if they leaked and ruined my marble floor, so the fact that I'm comfortable should say a lot.
You can see my set up in the link below and I am very happy with AP cages.