Do you have one of the black tank covers? If so, pull the cover off if it is direct sunlight on very hot days. The tanks are white.
It seems the safety valve is working as intended. BUT having propane gas venting anywhere it could collect or around any ignition source is a potential hazard, I would think.
You said that was last year. What is different this year? It has been very hot here in AZ recently.
EDIT: Ignore my post. Didn't know it was a Greyhawk. Assumed it wa a TT.
Sherm & Terry w/rescues Steve (std Poodle) & Eydie (min Schnauzer)
2015 Jay Flight 27RLS (Camped: 102 nights 2015, 90 nights 2016)
2006 Ford F350 6.0 PSD, Lariat, 4WD, CC, LB, SRW, auto., Camper pkg.