I had a 400 inverter and it was fine. I had a 90 watt panel. Am now upgrading to 100w and a 500 inverter. About all I use it for is a few lights, charging my computer and cell phone, and powering my furnace heater when it's cold. No problems yet, but I never tried to run a small fridge.
Only reason I'm upgrading is I sold the other with my old trailer.