The borate is not bad like a lot of other chemicals. It had been used medicinally for centuries, probably. Boric acid - anyone else remember it as an eye wash? It's also good at repelling roaches, termites, carpenter ants, etc.

If boric acid is applied to the soil, nothing will grow there, so it isn't to be used lightly, but it is affective in this application.

I agree with Bobert, the snow against the trailer will help a lot in keeping the temperature even. It's the reason you can stay warm in an igloo or snow cave.

SRS