2 heat-related rack questions

Ah-woo-heh-hoo! I ordered and picked up my Sintra (was not expecting that quick turnaround! very happy about that), wood, and 41qt tubs to start building my snake rack tomorrow.

So now, my two questions:

What size flexwatt should I get? I'm using 41qt tubs; should I get the 11in? I'd be using a foot of it as belly heat.

The flexwatt will be taped down on Sintra using aluminum foil tape, with the tub resting on top. The rack will be enclosed on three sides by hardwood panels, with just the front being 'open' for the tubs to slide out. Should I drill some holes in the hardwood on the sides of the rack? To provide ventilation for the flexwatt..

The rack will house my two snakes, plus probably another corn snake or two. Beyond that, not sure. I plan to wire each flexwatt tape individually so I can choose which slots have heat, or use separate thermostats should that become necessary.

I've got 3 and 4" tape underneath. If they had a little bigger I might prefer that. I know some people using the 11" put it in the back instead of underneath. You don't want too much of the floor heated, you want to create two temperature zones with some varying in between. My opinion.