How does he ride in the truck? If this starts the anxiety phase, you might try giving your dog something like Rescue Remedy, a natural calming supplement (available at health food stores). Our dogs will eat anything, so we just put some on a small piece of bread when we need to give them some.
Keep something on in the TT (tv or radio) to provide white noise, especially when you have to leave him for a few minutes. Keep blinds/curtains closed to limit visual stimulation, if seeing people/animals sets him off.
A tired dog is a good dog. Provide several walks a day. Since you're wanting to take him hiking with you, that should help a lot.
We take 2-3 dogs with us every time we camp. They've quickly become used to it and we all enjoy then experience.
Beth and Joe
Camping Buddies: Maddie (maltese/westie?), Kramer (chi/terrier?), and Lido (yellow lab)
2017 Keystone Bullet 248RKS
2014 Aliner Expedition Off Road
2013 Ram 1500 HEMI