Zoo Med's Reptitherm Mini (4 watts) can be used with plastic critter keepers. However, I'm not sure if the watts are higher than your present hermit crab heater to make a difference. Another option is to get an incandescent desk lamp with a 40-60 watt red bulb. Then you adjust the distance from the bulb to the critter keeper until you get the temp inside the critter keeper to 82F. Also, you can place the critter keeper(s) inside a larger tank and adjust the parameters of that. Good luck !