The flight plan form is really set up for IFR. Technically, you should
not use the /G unless it is an IFR GPS. It would however be a good idea
to add it to the remarks section.

The ATC controllers never see a VFR flight plan so it doesn't matter for
them. The VFR flight plan stays with FSS strictly for use in search and
rescue. Adding the GPS to the remarks section will help rescuers narrow
down your probable course if they need to go look for you.

Helen