I've had this problem with both RoadTrip and BaseCamp.
Fairly large GPX files imported into BaseCamp will cause it to freeze up. I get an endless beach ball, and Activity Monitor (and Force Quit) says that BaseCamp is not responding. When I make shortened versions of the gpx file, then it imports OK.
So, how big is too big? I may have to chop up the file into smaller imports, but I don't really know the maximum number I can import without is freezing up.
Steve