Abel Fotheringham

4’ Original slider - use manfrotto monopods to support the ends when using on sticks or dolly if there is no up/down during the shot.

I would maybe try a Mitchell vibration isolator on a Cardellini tri-hat with a low rotating offset from a Fischer dolly. You can use regular camera risers and almost get away with lead bags to hold it down. I always ratchet strap the base as well via any bolt holes or seat belt holes etc. Modern studio equipment make metric to 3/8' thread adapters which you can get 3/8" female eyes to rig into. Always keep the vibration isolator directly below the camera so that it works most efficiently. When the weight is offset it binds sometimes. I like bungee cams as well. I have a pretty cool setup that rides on a piece of pipe that takes out a lot of unwanted movement. That is the idea behind the vibration isolator as well. if smooth is what you are trying to attain then I would consider one for sure.

Or instead of painting it out you could just tip down until the top of frame lines up with the roof of the car. I would try to get an aerojib or aeroecrane in jib mode and mount say a libra head to it. You should be able to get away with a Fisher centermount kit possibly bolted through a couple of layers of 3/4" plywood or a large aluminum cheese plate . Rest it on some high density foam on the actual roof or build a pipe rig to mount it to the roof rack. Backwind the cables a coupe of turns reverse of the action and direction desired and get somebody brave enough to stand on the roof and step over the jib or rotate with it as it makes it's turns. If the grip wears a harness and isn't a complete idiot, it should be fairly easy and safe. Bear in mind turns add inertia so he would need to brace/prepare for corners. I personally would totally try it if you asked me to do it.

maybe you should consider mounting a jib arm on the roof of the vehicle and paint it out if you see it?