I did not read all the posts, so no clue how this discussion evolved (yet). If you want to find the actual square footage, then use a flexible tape measure. Simply lay it over the front end cap, from the bottom all the way to the top. The curved surface will be longer than the flat straight line distance from absolute top to absolute bottom.
Once you have that measurement, just multiply it by the width. Is the width slightly curved too? Mine is. Well, simply measure the entire distance with that same tape measure, letting the tape measure cure on the surface. This will be the actual size. Now, multiply the 2 figures together and there is your (surface) square measurement (inches, foot, yard, meters, whatever measurement you are using).
Now, if you are not in possession of the camper and can't do this, then I have no clue how to find your answer.