I'd rather the think get a fuel cost.
I don't think this would solve the issue, since it only takes one Kubel to seriously screw over the USF from the get-go, with the help of truck push and sturms- unless the fuel cost became inordinately large.
I'd think that having the Kubel remain exactly as it is now, but only buildable after the first truck is deployed, would be the ideal solution- that way the OKW has a manpower-only suppression unit that isn't terrible in the later stages of the game because of slow speed or rotation or pack up time making it roll over and die to AT guns, but would also avoid the 3 minute kubel-at-your-cutoff syndrome that makes USF so annoying to play. It would also require least changes to the unit itself.
At the same time it also allows the OKW player to make a more strategic choice- rushing out the Kubel would cost 440MP and 40 fuel, but theoretically can be done right out of the gate, so there would be tradeoffs involved- impactful unit that requires a tech decision early and fewer supporting units.
Also the vet 1 ability can't remain the same, it outclasses the Sauron halftrack and the million units with infantry awareness so hard it isn't even funny. I don't even see why it shouldn't get a clone of the infantry awareness ability, as boring as it is.