I agree with deputydog. You will get many different opinions on this one. I have all mine mounted internally, but I'm flying larger airplanes and have more room inside to keep things clear of any interference concerns. On my gas engine model I mounted the antenna externally as an added precaution.

When first setting up a model I always do a range check with the engine off and then on. After this initial check I always do a range check with the engine off before my first flight at the field. If I suspect a problem I will revert back to doing a range check with the engine off and then on again. Always fix any interference problems at the first sign of an issue. Never fly the plane until you are confident the problem has been resolved.

When mounting the Rx. try to keep the antenna as straight as possible and avoid allowing it to curl up at the end. Don't wrap it around anything. Avoid going one way and then doubling back when routing from inside the fuse to the outside.

Just don't take the short cut of not doing a range check before your first flight at the field. This is a critical step that you don't want to get lazy with.