If ur up for a little DIY, I drill a hole size of sensor into the thickness of the base of viv from back toward front. Then from inside (obviously knowing your measurements and where your hole is) drill down to meet hole. Your stat is then underneath your mat just touching. Then hole through back for mat lead. Use sealant to stick mat down.
Now if your not a DIY man then don't do it as it could go horribly wrong!! :gasp:
Just means snake cant move mat or sensor and it's all lovely and tidy! Not that i'm OCD! :whistling2:
Like others said use thermometer to get temp right.