Teaching your dog to jump in the back of your car or truck is very simple. Start with teaching the place command on something closer to the ground, such as a dog bed or rug. Then teach with something like a cot or short retaining wall. Then add something a little taller, like a weighted, medium sized dog crate or a weighted cooler. Add taller things slowly–especially if your dog does not like to jump. Make it fun. Use lots of praise and add valuable treats. Here is a video I did last year with a five month old puppy.