Thats the main reason I hate using externals on packages I put up to sell.  It can get confusing to novice users.  I solved the problem anyway.  I just made two separate .car files, one had the Lighthouse and cottage, and the other had all of the environment stuff like the terrains, pier, stairs, rails etc.  I managed to get them to about 27MB each and I'm uploading right now as a a matter of fact.  Morte of a pain and larger files, but they are pretty much foolproof.