I find a good thermometer/hygrometer helps with the whole keeping a temperature steady. After a little practice and having a few different heating options it's a lot easier to keep the temp in a steady range.
I'm a little confused about the "above 80 is dangerous" thing. I live in an area where these frogs are native and it often reaches into the high 90F's/ low 100's in the summer. True, in the whole outdoors there are probably a lot more cool places to hide than in one small tank.
Also it may be that temperature extremes can be disruptive to frogs and just because they can survive in high temps doesn't mean they won't get stressed. Stress can be bad especially for wild-caught frogs.