Much was improved since starting this topic. See the developments in this topic:
So Agopengps v4 can create a precise boundary and KML now. Once a boundary is created you can pick up the KML file in the field folder and save it forever. Great!
I have built a handheld receiver similar to that of Ardusimple and I plan to use SW maps (Android) to quickly register points of interest throughout the season. Maybe boundaries too if you want to do them by walking. It lets you register continuously or specific points. It exports Shapefile, KML, but I have yet to try if the line feature KML imports in Agopengps well.