You can counter-condition with the destination instead of treats -- but keep the rides very short (not 6 hours) and frequent (several times a week). Frequent, very short drives to a dog-park or safe, fenced field for a rousing game of fetch turned into a great reward for one of mine that didn't like to ride but loved to fetch off-leash. Now he thinks every ride means going somewhere super-fun, so he's happy.
Frequent, short rides (like just around the block, to start out) help de-condition the nausea some dogs get too. I had one that always hurled in the car on short local trips who now can ride cross-country on multi-day car trips -- we worked him from trips around the block to short trips to good places.
Last edited by Magwart; 10-19-2019 at 09:03 PM.