The best way to photograph RC airplanes is to follow the plane while shooting in continuous mode. You cannot do this with any kind of electric viewfinder since all you see is black between shots and you lose the sighting. You can get some cool background motion blur this way. See the pic at the bottom of this post.

A tube hot-melted onto the camera is a good idea if you don't have an optical viewfinder.

Also, you need a 10X optical zoom, or the equivalent of 300mm. And if you want to print anything 8x10, you need 3Megapixels.