Even with a heater, a vintage trailer can have cold spots due to incoming drafts. Here are a few tips to share about upping your comfort level.
1. Insulate the roof vent. Heat rises, so you know what happens when your heater's work hits the roof--it's pulled right out from that uninsulated plastic or aluminum vent cover. Basically, you have a hole in the roof. To block the hole, cut a piece of foam to fit, or spend about $12 to buy a covered foam
vent insert from an RV supply store.
2. Drape the door. I have an old woolen serape that I use for this purpose, using clip rings on a rod to hold it up. I leave a few extra inches at the bottom to block drafts at the lower edge of the door. Use your imagination to come up with something similar that will work in your trailer. You may with to do something similar for your trailer's larger windows.
3. Bolster the bed. A trailer bed always ends up somewhere along an outside wall, and if it's over a cubby space, it's also resting atop trapped cold air. To cut the draft/chill factor, bolster the bed with rolled-up blankets and extra pillows.
4. Use a good sleeping bag. The whole glamping thing is great, with adorable bedding, ready for magazine pages…but when the camera's back in the case, warm is where it's at. I've never, ever been cold in my sleeping bag, even with no external heat whatsoever, even below zero. For cold weather camping, it comes along.
Note of caution: If you heat your trailer with propane, don't seal it up too tightly, and keep a carbon monoxide detector inside.