I have added a GPS popup window using an FSX default GPS. The panel cfg file adds the window the easy way by copying the default J-3 window data entry for the GPS. The window number may need changing. That is the basic idea.
But if I try to fly IFR in the worst weather, such as icing, heavy fog, and at night, then common sense says I should not be in the air at all. It depends on how realistic I want to be in a traditionally VFR aircraft.
But for those who prefer a GPS there is a way to get one.
Cold winter air for one screenshot, Tongass flightseeing, the essence of VFR.