Just in case anyone else is still considering an underbody LPG tank, I just installed the 4.6 gal 8” GoWesty tank on the drivers side. It fits between the wider “east-west” frame rails, and is totally invisible from view when standing alongside the van. I bent the thin single-wall frame brace so the tank could fit higher in the cavity. We’ll see about filling, but I don’t anticipate a problem. Stout brackets were welded to form 2 “C” brackets from two 2”x3” and two 2”x2” L brackets (I think...they were scraps).
I chose the smaller eurovan tank because it fits between the stouter framerails, and is in fact bolted to them. I fished six 1”x2”x1/8” plates with welded-on 5/16” grade 8 nuts into the frame rails, using existing holes in the frame rails (plus a 3rd hole drilled into the more forward rail. So each bracket has 3 bolts going into the frame rail, and 2 bolts into the tank flanges. My welder buddy bitched and moaned the whole thing was overkill, but I think the 3rd bolt was key (Sportcoupe had just posted his pics of his Helwig sway bar mount ripping his frame rail, so I got nervous). So, in effect, the tank flanges are ~ 2.25” below the frame rails. In retrospect, it might have been acceptable to hang the tank 3/4” lower, but it would have been that much more vulnerable to rock hits. BUT, at 3/4” lower, I might not have had to bend the single-wall frame member, and could probably have fit the 5.9 gal GoWesty tank. It’s also possible the 10” tanks currently on eBay would fit like mine, though hang lower (or you could mount them higher into the frame to compensate...again, I think they are short enough, though you might have to trim the mount that comes with the tank....but that’s just speculation
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