Advice/tips on car set up for my pup?

Hi, I'm just looking for some advice on the best way for my puppy to travel in the car.

She's currently 5 months old, I took on her on quite a few car journeys to try and get her used to it when she was younger but she still struggles.

If I'm driving, I usually have her seatbelted and sat on the passenger seat, but she constantly pulls over to me, whines and seems distressed. If someone else is driving we sit in the back seats together, seatbelted in still, but pretty happy on my lap or looking out of the window.

I really want her comfortable for longer car journeys as I'd like to travel/camp with her. I have a little self converted camper van, but there's not really any space for a crate in the back.

Any advice on set ups/kit would be great!