Welcome to the Sunline Owners Club (SOC). Perhaps you will be able to find someone in your local area who will respond who would be able to look at the trailer you are looking at. There are many very capable people on this site who have answered many questions for me. Is the Sunline being purchased privately or through dealer? Hopefully the present owner can demonstrate the electrical, heating, and other systems so you know if they are operational. You will want to look for soft spots on the floor, discolored areas on the floor, walls, or ceiling, if possible take a look at the roof to look for areas that are damaged. Do the cushions, cabinets, look like they have been abused? How about the exterior, siding, tires, lights, frame members, anything bent, welds broken, etc. If AC power is available you may be able to check the power converter and appliances.
You will not be able to check the water system due to freezing.
Again welcome and good luck with the 1992 T-185. We had 1992 T-2251 for 20 years and lived it.
Paul and Nancy