I just went through the same dilemma when I had to replace a heater in my 150 that broke. I decided to replace it with the same heater that I had in the first place. They are bullet proof, turn off when you drain the water and the electronic temp control is not attached to the heater, it is what plugs into the wall.. You wont have to get your hands wet..
I bought a 500watt one for my 150 but you would be fine with a 100 watter or maybe even a 150 depending on the ambient temp of your house. You can find the 100 watt one online for under $30