Umm, I probably broke the rules then.
I twice went for a max duration flight using a sailplane equipped with a long range radio to allow smoother flights at higher altitude.Note this is only under certain conditions, and using a rough method of angles, trig, and timers we determined that the aircraft exceeded 1500 feet AGL, or 7500 feet MSL.
This is done with a spotter, as well as a "the plane is expendable" attitude. Aka, if anything appears on the horizon, the plane dives to ground level and lands. This is not, I realize, following the AMA suggestion that aircraft be kept below 400 feet AGL, but it was also not in the vicinity of an airport. The nearest is approximately 15 miles away.
It was fun, but after the first dive, I quit, and do not plan on trying a high altitude duration flight again.