I just had to order another receiver because I killed my antenna and lost a lot of range. Can I leave the antenna on my new rx inside the body and still have great range ?
No, not a good idea. Put the full length of the antenna in the tube and just bend it back or to the front or side when putting on the body. You want it extended, but inside the lid is no problem.
The reason it should be in the tube is to keep it from getting caught on any moving parts in there.