Sorry you're having trouble, Reinz.I agree with you, I didn't find my PVC enclosure to be "plug & play," either; I was having the same issue with mine. Luckily, I'm keeping a Brazilian Rainbow Boa in mine, so he loves/needs the humidity anyway, but I was less than impressed with the radiant heat panel, too.
What I ended up doing was using the RHP on its own thermostat to keep the ambient temp at 75, since my house is on the cool side, and then put a 1'x2' rectangle of Flex Watt underneath to create his warm spot at 83, on a separate thermostat. Works amazing now, but definitely was annoying to set up and not as cheap and easy as I thought.
Hope you get it to work out for you. On the bright side, the girls are looking beautiful!!