What sort of evaporation? If no vapor is being drawn nothing is leaving the tank.
Propane should not evaporate from the tank. That would sure create a fire danger. Maybe a piping leak, might want to have it pressure tested. Have the propane supplier check all fittings on the tank with soapy water.
My neighbor is on auto fill and the propane truck seems to put more than a few gallons every month. I always prefer to call when I need gas. They are happy to bring a 100 gallons or more anytime.
It’s not a lot but there is some
I believe he meant to say expansion, and they do not fill a propane tank over 80% here in Texas, because if they did so, during hot weather the “pop off” valve would trip and let the gas out.