Consider a propane heater like Mr. Heater. Most electric space heaters are going to use all of your 15 amps by themselves. Adding more power is going to take an electrician or someone familiar with electrical work and willing to rewire your trailer.
Find the ratings of all the stuff you are running and add it up. You can convert appliances with watt ratings to amps with a simple formula.
Amps are watts / voltage. 200 watts / 120 volts = 1.67 amps for example.
Add up all your stuff, including the fridge, to see how much power you need. Anything that creates heat from electricity is going to be a power hog: electric heater, coffee maker, hair dryer, and that warming plate. Right behind that are compressor motors that use a lot of power to start. This includes refrigerators and air conditioners. I'm not at all surprised you are blowing breakers with a heater/ac unit and a warming plate.
Once you know your total power consumption, you know how big your panel needs to be. Common sizes for trailers will be 20 amps, 30 amps, and 50 amps. You have a main breaker that limits the total power coming into the trailer, and one or more breakers for power distribution to the outlets. Changing out the panel alone won't help, as the wiring to the outlets and the outlets themselves aren't designed for more than 15 amps.
So to add more power, you need more power coming in via a 30 or 50 amp panel AND more circuits to distribute that power. You are going to have to do some rewiring here. Even with a 30 amp panel, you would need to rewire the outlets so that no more than 15 amps travels over a given set of wires. If you have, say, 6 outlets you might want to rewire them so no more than 3 are wired together.
Propane heater might be easier. :becky: Yes, this is a job for an electrician if you aren't comfortable doing that sort of work.