I have used an old dish washer for the last few seasons. Worked great! Last season I upgraded to an old 1960's type fridge/freezer. I gutted it and used the same heat tape and thermostat out of my old dishwasher incubator. I use wire type closet racks and a tub of water at the bottom.
The problem I had was with the fan. I could not get it right. I ended up cutting 2 vents at the bottom of the door an a 2" pvc vent pipe at the top. It ended up working perfectly with no fan.