It's been done.
But the shortest model you will likely find to purchase is about 9.5' long. The back has a peel off glue strip that would probably degrade after awhile. Although changes to the backing wouldn't degrade performance.
Personally I would install a smaller rigid panel instead of messing with unisolar that doesn't fit a rooftop. The advantage of unisolar is that it disappears on a large roof, and has little chance of damage. It also seems to have good performance with less than ideal sun angels. It's a good "install and forget" choice.
Rigid panels have a considerably better power out per panel area.
We're getting closer to having glue-on flexible panels with high output at a low cost. When that happens we will all be putting flexible panels onto the open spaces on camping vehicle roof.
If unisolar made a half length panel these would work well for typical 4x4 vehicles.