Please recommend an all-season travel trailer with bunk bed?

Check out the Evergreen I-Go 256RB. Easy towing, light, and good build. They are a little narrower than most but have a deep slide. They are also insulated between the frame rails. Down to freezing and with four people in it you should be able to heat it with a tiny electric heater without the furnace coming on. They use a lot of on demand hot water heaters too; nice for long hot showers provided you are hooked up to the sewer. It's a real luxury in really cold weather.