Mike Noel wrote:
At airports that don't report altimeter settings I set my altimeter
according to my GPS altitude and this has given me a reasonable
ground MSL according to the published altitude of the airport.

How is this better than the traditional way of just setting your
altimeter to indicate the published field elevation?

THere's only two reasons you want to know your altitude. One is to
know how high you are relative to the ground, the other is to know how
high you are relative to other airplanes. Setting your altimeter by
the GPS gives you neither.