We're probably talking about a max of 100 lbs including the trailer itself and insofar as drag is concerned the trailer is nicely, neatly, tucked in behind the towing vehicle's wind shadow, drafting as it were. Not that the trailer would have enough frontal profile to create and significant level of drag to begin with.

And keep in mind that the CNG is being compressed from your natural gas supply at home, relatively inexpensive and NO road taxes. Inverter style gensets operate at whatever RPM level the demand load dictates, Idle when the batteries become fully charged.