We live in an apartment with vaulted ceilings and a really underpowered heating unit, so it's freezing in winter. We got an oil-filled radiator space heater and it's pretty incredible how effective it is at keeping our apartment warm. You can find one for ~$50. They use less electricity than infrared heaters and are much safer. If you live in a trailer, I imagine it would drastically improve your situation. Its cheaper than an HVAC unit at least.