Try using a target area in the back seat Loki is to stay on. Just as an example, say a cheap bathroom rug. Use it to train him in the house...have him sit on the rug and remain there till you release him. When he is really good at there, move the rug outside in the grass (or porch etc.) When he is confident at that move the rug into the back seat of your car. Go from you standing outside of the car, to going to the front seat - to driving down the drive way...etc. Take baby steps with him. Don't expect perfection. Make sure you reward with a big happy dance when ever he does it correctly, even if it's in the house. Every once in a while go back to the beginning (in the house) to keep his confidence up. Always reward!
Hondo Von Dopplet L Bauernhof "Hondo"- GSD
Lilie's Tug McGraw "Tug" - Golden Retriever
Maggie - Mini Dachshund (Rescue)
Lonestar Pivo - Texas Blue Lacy
Ashe - Barn Cat
Katie / APHA