The chemicals can freeze and damage the unit. A lot of these are designed to be emptied at waste disposal sites for camper trailers. Most homes don't come equipped with RV dump stations. It is better to have a permanent outhouse style commode so that you don't have to store, handle, clean buckets, and dispose of the waste. Outhouses I believe this to be the best way for human waste disposal in long term emergencies.
Outhouses are easy to build.
The average outhouse should be about 4ft. square by 7ft. tall. They are just a wooden box with a roof, a shelf, a floor and a door. The wall with the door in it should be 7ft. tall, the opposite wall in the rear should be 6ft. tall. Of course the side walls will have an angle across the top. When you frame the floor, don't sheet it until last.