I can chime in on heat sources since I have used belly heat (flex watt) as well as radiant heat panels.

Two of my three boas hang out on branches above the floor and one burrows under aspen a lot. I used flex watt in the 2x3x1 cages from RBI and I was not able to keep the floor temps at 91F and still have the temps correct for where they hang out above.

I switched to radiant heat panels for all three cages and I believe that it has made a big difference. Not only did it provide a bump to my ambient temps (which was needed) but the RHP's mimic the sun and allow for a greater temperature gradient for the snakes to thermoregulate within. As in nature, if they want to cool off, they can go into a hide or under a branch or 'out of the sun' in some manner that I have provided (such as burrowing in aspen!)

When the snakes are upgraded to the AP T20's, I'll continue to use RHP's