brao.....You don't say what coach you have or if it's a 30 or 50 amp system. Most any heater will work well. I went to WalMart and looked at several they had on display. There was an outlet near by so I plugged each one in and found the quietest.
For those with large whole coach inverters, you should know which outlets are connected to your inverter and which ones are not. This is easily done by disconnecting from shore power, turning on your inverter and checking each outlet for power. Mark those that are not on the inverter system (have no power) with a dot from a Sharpie. The reason for doing this is to prevent wear and tear on your inverter. Even though your inverter may be off, all power into the coach runs through the inverter (bypass system) and then to the outlets you didn't mark. Running a high amp item like an electric space heater through them for long periods of time is not good.
Try to use the plugs you marked with a dot for your heaters if possible. These draw power straight from shore power through your circuit breakers.
If you use space heaters a lot and you have a 30 amp system or camp with only 30 amp shore power, here is a good project. I ran Romex through flexible plastic electrical conduit (available at HD and Lowes) from a box in my power bay, under the coach, and along the frame to a separate outlet I added in the living area and the bathroom. At the box in the power bay, I connected a heavy duty section of power cord (about 20') and a heavy duty 3 prong plug.
When we are going to be running the heater for a long period, we connect this cord to the 20 amp plug in the shore power box and use it for the heater only. We use the non-inverted outlet in our bedroom for a second heater that is running through our main power cord.
This cord addition also helps when you only have 30 amp service. By plugging in the added cord, you can run the heater without using up any of your 30 amps from your main power cord. I also have my wife use the extra outlet in the bathroom for her hair dryer when the heater is not on.