Onboard chargers have to be plugged in to 110 unless you can run across some sort of solar deal or one of the ones that charges through your vehicle's charging system while trailering.
I bought a Guest from Cabela's on sale a couple of years ago that has been well worth the money. Looks like they have the same charger $10 cheaper now than when I bought it 2 years ago: https://www.cabelas.com/cabelas/en/templates/product/standard-item.jsp?_DARGS=/cabelas/en/common/catalog/item-link.jsp_A&_DAV=netcon&id=0022981016459a&navCount=1&podId=0022981&parentId=cat600056&masterpathid=&navAction=push&catalogCode=9IS&rid=&parentType=index&indexId=cat601233&hasJS=true