You may want to check out the validity of international flight training. I'm not sure that it really counts unless you're in Alaska or something... I could be totally wrong but you may want to reference that. It could make or break your adventure (or really the logging of it). Generally the FAA would not see the validity in a 300nm intl xc for an add on rating. If it is a commercial you are working towards...I think the xc's have to be domestic (at least in the conus)...
Could be wrong (it wouldn't be the first time) but just reference it...I'm too lazy to right now.