Like someone mentioned, finding a 4 season trailer is going to be almost impossible with a budget of $5,000.00. The rig I'm living in is a entry level Winnebago Motor Home, and it can be done. If your planning on heating the rig with the onboard furnace good luck. What you need is one of those wave-3 propane ventless heaters. More than likely a 6,000 or 9,000 btu unit. The use a whole lot less propane. As for as the A/C unit you'll need as least a 15,000 btu unit. A 13,500 unit just isn't going to cut it. And a water heater with an electric element. Good luck