I'll leave the GPS questions to those who know lots more than I do, however, the following statement begs a response...
> On all my future trips I'll be dropping stashes off ..cool...
If your travels return you near to your placed stashes, by all means stash away! But I'd refrain from placing any that you know you can't get back to check on at least once every 6 months.
I'm curious how others feel about stashes being placed that the owner can't readily maintain. I'm one who believes the stash's owner should be able to visit his/her stash on a semi regular basis to periodically verify it's existence and integrity, and to inform Jeremy and anyone else necessary if/when the stash no longer exists at the specified location. It's no fun spending the time and energy searching for a stash that may have been plundered or destroyed by the elements, etc. Searchers can't really determine it's existence as they might just not be able to find it.