I don't have a Westy....but I've got a nice tintop with a roof rack for cargo box.  Extra fuel could go up there.  But as I mentioned previously, I'm sorta giving up on the extra gasoline thing.  Not needed after 30+ years of practical experience.  Have never run out; and in time it just goes bad, so some hassle for exchanging with fresh fuel.  Maybe if I went to Alaska....but that's not going to happen....mosquitoes the size of hummingbirds!  Not to mention all the front sheetmetal and paint damage and windshield too.  If I go to and from Alaska, it's going to be via a boat and airplane.
Rich
San Diego

    On Saturday, January 4, 2020, 5:46:28 PM PST, Cunegonde <cunegonde.van.westfalia@gmail.com> wrote:  
 
 While on long trips, we use one or two portable 5 gal marine outboard engine horizontal tanks, strapped down firmly with webbing, in the luggage rack. They of course have hoses which reach the gas cap. That way don’t have to bring them down to refuel. Alas, rarely will fuel station filler hoses *fill* said tanks while still up there.