When I was sizing my LP tank, I cut pieces of PVC pipe and/or sonotube of various diameters and lengths to mock up what my tank size options would be so I could physically see what it looked like in the space.
2009 Express AWD, CCV Top & 50-ish home build. Daily driver/camper/kid hauler
I think it said 36" long. Not sure where that would even fit under the van. There is a space behind the diff on the EB that might work if it was around 33". A remote fill point would solve the accessibility issue.
Beastie 3: 2002 7.3 EB Cargo: Agile TTB, CCV Mid Top, Custom Walk Through, Lots of stuff added. BlingMyRig.com