After trying it this way and that, I settled on a round bubble level, double sided tape attached to a flat piece of aluminum. A magnet attached with duct tape holds it to the Scamp
frame where I can see it when turning the crank. The way the first picture shows it, a single piece of a 2"x6" scrap wood under the right wheel would take care of it, front to back is good as is.
Actually, the part that needs vertical alignment is the complicated plumbing behind the fridge, where those nasty fluids (ammonia being the worst, then hydrogen, then water) have to flow down by gravity and then are boiled and pumped up against gravity. If it is tipped too much and the flow is impeded, it is a no go. So we should be aligning the plumbing, but we have to settle on leveling some other features of the Scamp
Note for the picky ones: I know the frame needs a coat of black Rustoleum - it is on the list....