Our fur-kids also get the back seat sans harness or crate.
When we bought our first truck... 15 years ago, we had to get a king cab, so our 180lb rott/shep/pyranees mix could have space to sit inside with us.
Our new truck is a crew cab, so the dogs get their own doors, now, too. We flip the back seats up, fold down the platform and put down a non-skid pad topped with a fur-covered foam pad, and the dogs hop right in. Once we get rolling, the older one (Zedd, the brown one) likes to watch out the window (for a while, anyway), but the younger one (3 yo in the picture) just passes out. Great travelers!
We put a flannel bed sheet over the seats to control some of the hair... but still need to find some seat covers for the back of the front seats... There's always more hair!
We also have a "no-spill" travel water bowl for them (shown in the picture with the black dog, Chase), so they can have water in the back seat of the truck. It works well - unless they step on it and flip it up-side-down... then it WILL spill.
They know not to get out of the truck until invited to do so. But, a harness would be a good idea to keep them safe in case of an accident.
PS - We found a new home for Chase due to some other issues, so Zedd will be getting the back seat to himself now.