Steve Flynn

Correct I meant 3000 watts.  

Its a complex formula to measure properly how much heat is needed for any room or heat type.  You also need to take into account insulation R factors.  A 7 to 8 foot ceiling is the rough height I was assuming, so using the math you should be covered, however there are two exceptional factors that will cause you to feel cold if you are using these in a shower scenario.

The first issue is that in a shower scenario you would be more prone to feel the coldness of the air.   One of the reasons for the efficiency of these panels is that it uses far infrared based heating which works similarly to light.  The efficiency gain is from less heat energy is absorbed into the air.  Think of them like an efficient heat lamp.  

The second issue that will make you feel cold is that you will only be heated on the side of your body facing the panel.   To properly mitigate this issue and to feel comfortably warm you would need one panel on each side of you.  With these two panels you should feel the warmth on both sides of you.  One other aspect is that the heat coming off of these panels builds slowly.  I would recommend turning it on at least a half hour before using the shower.

I have a ton of experience with this technology and find that if you do use these you would want one on each end of the camper.  Where typically with electric baseboard, you would need 10 watts per square foot of heater capacity, with these you only need 6 watts per square foot of heater capacity.  That being said if you under power a space with these though, then they do not work too well.   So if you have 500 square feet of space you should have about 3000 square feet or 6 of these panels to cover the space.  That is still significantly better than what electric baseboard offers.