If it works like the Honda, you can use all the receptacles at the same time as long as the total load does not exceed the gen's rating, or an individual receptacle's rating. For a 20a load I use the "30a" (23.3) receptacle instead of one of the 15s.
I have an adapter that goes from the shore power cord 30 to the gen's twistlock 30.
You have to juggle receptacles for what will pop who's breaker, between the ones on the gen and the ones in the rig. Soon discover what you can get away with!
๐ (as when I had my several Vector chargers all going at once--where to plug them in? )
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.