I've wintered my glider outside in the PNW, but it is NOT preferred. Of course, it is best to put your trailer under a carport or, if possible, in a garage (which is where I store mine now and would never go back outside).

Gently heating the inside of the trailer is a essential. Be careful with all heat sources. Electric heaters should have auto off in case they tip over for some reason. They should have some type of insulation from direct contact with the trailer (bricks work nice). Light bulbs have been known to cause fires, so I would avoid them. My preference is a chick incubator available at your local rural hardware store. It is low voltage and usually insulated.

Air flow is essential. Don't plug up the vent sources.

Dri-z-aire needs regular attendance. Follow the instructions provided.

Good luck.