That would be a NEMA L6-30, which is a three prong 250 volt with two hots and a ground. I like Leviton products. Their car mount flanged plug is their #2625F.I'm using the 30 A locking plug, because I could fit it easier than the dryer plug, and I could buy a 25 ft extension cord for generators at Home Depot with matching plug for $65. My pack is max of about 124V at end of charge, so I only draw about 16A from a 240VAC outlet when charging at 30ADC. I also have a PFC30.
By the way, doesn't your PFC30 cut back at 30 amps DC due to being thermally challenged? Seems you discussed this some time ago.