Any advice besides the usual on carsickness for a 5 month old puppy? He mostly drools, but I see he is starting to dread going in the car.

Just keep taking him and make them short rides to a fun place - a park or something. And bring paper towels and a garbage bag...
One of my guys was VERY bad when he was young. Would vomit every single time he was in the car. When he was 8 months old, my dad was very, very sick but wanted to see his "grand dog." It was a very long 400 mile one way trip but we made it. The dog never got car sick again. The ride home was fine. Maybe he was desensitized on that trip.

I have found that riding closer to the front of the car helps puppies (and me). I have a crate in my van that is sidewise behind the passenger seat, and the ones who have nausea generally do much better there than in the back. Also no feeding a couple of hours (at least) before the ride.

Send me your email address & I will send you a doc with instructions.

I had good luck with ginger capsules. You can get them at your local health food store.