I love what you have done. Your very handy and thanks for the very nice write up and the good post!
Is there anyway to add a roof vent to your TT? Even if it's a small one? Like say a piece of 3-4 inch PVC pipe? I don't know if this would help but, I wonder if that along with your modifications would do the trick. The roof vent would get the "stack effect" started and once you got the air moving through the bottom of the fridge then your fans would be able to pull the hot air out .
I have no idea really. I'm just bouncing ideas off of you and all of the other member to see what you think.