I can imagine how worrisome that was. Our office dog, Hunter, pants and paces the office like that when his "mom" isn't in the office. He's 15; an old Golden Retriever. Part of my favorite work duties is to take Hunter out on my smoke breaks to potty. But I digress....
It will take practice for Ollie to get comfortable in strange places and the only way to do that is to practice by DOING IT. Why don't you go for more frequent - but shorter - trips places?
When it cools off, perhaps you could try a "Thundershirt" or some "Rescue Remedy" (I believe it's natural oils or something) to help calm him on these outtings?
I'm curious of the other dog was avoiding him. If he was genuinely in an anxious state, I would guess that the Boxer steered clear of Ollie in that case. Just curious.
When I first started taking Bea and Bo together in the car, at one year old, Bea was already a seasoned traveler. She gets in the rig and settles right down. When we get to our destination, she makes herself at home. She's been a great example for Bo -- who tends to be a bit more (LOL!!) excitable.