5 gallons is too much for us, too. The steel safety can we carry in an outside storage compartment in our small Class C is actually a 2 gallon version similar to this one:
https://www.amazon.com/Eagle-U2-26-SX5-Safety-Flammables-Capacity/dp/B002M3DY9W/ref=pd_day0_hl_86_2/138-8614902-3914606?_encoding=UTF8&pd_rd_i=B002M3DY9W&pd_rd_r=691c940f-12b2-11e9-912d-b5f71776edbd&pd_rd_w=MneRI&pd_rd_wg=eZWmP&pf_rd_p=ad07871c-e646-4161-82c7-5ed0d4c85b07&pf_rd_r=NA0XG1F63KRB9RSSTB0Q&psc=1&refRID=NA0XG1F63KRB9RSSTB0QThe little 650 watt Honda we use for additional drycamp battery charging options carries 0.51 gallons and will run for 5-6 hours on that. Leaving home with a full Honda tank and with two gallons in the steel safety gas can, we are set up for five 5-6 hour running sessions with the portable generator.
What we wind up with is three noise level choices for non-solar battery charging. Loudest is the built-in Onan, next quietest is the Honda, and quietest is idling of the main engine.
Probably the Tech forum would be best for RV gasoline transportation information.
