Hi All

Your frogs are most unlikely to burn themselves on a heatmat mounted outside the tank.

I've always used heatmats and , thus far, have never had a problem!

Personally I have just invested in some higher wattage (30w+) heat mats and a couple more thermostats for my current collection and pending Dyeing Dart Froglets!

Alternatively if you provide a large water section for your frogs you could pop an aquarium heater in there and stick it on the highest temperature - the evaporating water should help heat the tank a little - but not to the extent of a heatmat!

(Also to improve heat retention from a mat consider mounting card over the side it is on - and the other sides of the tank to improve insulation - every little helps!)

Hope some of this helps!