I am not a patient person, so for me the direct approach is usually the one I use. When Jake got scared from all the fireworks, last July, he would not go into the back yard at all. I put a leash on him and drug him out 3 times a day and stayed til he did his thing. After a week, he understood, if I told him to come on, he might as well go. When he still was not happy out there, he got fed out there. Moving the bowl further and further from the door. After a week, he would go out voluntarily and finally figured out that playing and running in the yard with Max was almost as much fun as running through the house. I would simply put a leash on him and drag him to the truck. Once I got to the truck, I would open the door, put him in it, literally picking him up, one end at a time. Then take him for a ride. If he settles down quickly, once he is in it. Stop a few times and let him out. Each time putting him back in, after a minute or so. Go by Macdonalds and buy a burger. Feed him little bits of it. This way,
1. He understands that you are in charge.
2. He has a good time, when he does what you want.
3. The truck is not going to hurt him.
4. You are not going to do something that will hurt him.
5. The truck now signifies good things.
Just my 2 cents worth.
Kathy