Hey man. I'm already excited to see how your project turns out! I personally have a boaphile sideways rack. The flexwatt goes lengthwise like you are talking about, and I like the gradient, though I think my tubs are a bit bigger than the ones you are talking about. As of yesterday (I'm not home, or rather actually home and not at my apartment, haha) the heat tape temp is at 93-94 and the cool side is 80, with 60-70% humidity. Those numbers are ridiculously solid, aside from the humidity. When ya spray it spikes, then drops to the average.

None of my snakes seem to have a problem thermoregulating in the rack. As you can see in the video I'm using litter boxes for hides, there is actually a warm and cold side (ish) to the hide. If they want something in the middle, they lay on top of the hide, and the coolest is at the front of the cage.

I took this video a couple months ago. The audio got all messed up. It WAS seamless, but oh well. The first part shows the rack. I'll take a couple pictures for you when I go home tomorrow. Let me know if there is anything on it you want to see!

YouTube - My Ball Python Collection, Rack, and Some Feeding!