Did an update to 0.8.186.801b of GMaptool. Followed catymags link in #40 and found that it was in fact a very simple operation.
Was successfully creating a TYP-ed map, that was accepted by both my GPSr and BaseCamp.
Looks like the pietu procedure (that I tried earlier), referenced here in post #4 of....:
[Only registered and activated users can see links. ]
....is changing things that screws up BaseCamp. In my Oregon 600, it was operational.
Thanks everyone for the support.