Hi,
He's not using a UTH.
I can't decide if insulating the enclosure would stabilise the temps or if you actually want to increase the ventilation to stop the cool end heating up that much.
It's hard to be certain what is actually happening but I think the herpstat is doing its job but the ambient heat built up in the viv isn't dispersing fast enough for that to keep the cool end stable.
Anyone else have any input on this?
dr del