Wavian is what I used on my roof as well. Didn't like having it up there, but it was either that, inside the vehicle, or spend $1200+ on a bumper with swingout/hitch tire carrier/etc
Went from sea level to 12,000 feet, no leaks.
I've used my spare fuel a couple times. Once because a planned fuel stop was closed, the other was because I was a dumba55 and forgot to fill up prior to starting a trail.
I almost needed spare fuel on the highways/back roads between Boise ID and the Oregon/California border last summer. Took so many back roads, I ended up unintentionally going around most gas stations. I was on the highway, another one was bound to come up soon, right? I eventually turned around and drove back about 15 miles and detoured another 10 miles to a town with a gas station. I was 10 miles past "0 miles remaining" at the time. Super fun.