Fear free meds-next steps

I have a 4 year old cattle dog/border collie mix who is just the sweetest, most well behaved dog you’ve ever met… until we go to the vet. He’s about 70 pounds, and we’ve tried many different doses of fear free meds for him (combos of gaba and trazodone) and he still can’t even get a simple vaccine at the vet. It’s to the point that when he’s dosed with gaba/trazodone he gets MORE anxious, possibly because he associates that sleepy feeling with going to the vet now. I dosed him for the 4th of July like I usually do (which is a lighter dose than his last vet visit), and he did worse on the meds than I believe he would have off them. We have a slightly bigger female dog who took the same dose for the 4th of July, and she slept through everything, my boy was wired and shaking like someone who drank too much caffeine.

We have tried to get his vaccines updated 4 times now, all have been unsuccessful. All have had progressively higher doses of fear free meds. His vet is fear free certified. I have just refused to take him in and keep putting him through that for vaccines at this point, the vets office keeps calling and sending post cards reminding us to bring him in to update his vaccines.

What could our possible next steps be? What would we ever do in an emergency situation? Luckily we’ve never had to take him to the ER, but if we do I am not sure how to navigate that. He is having some non-urgent digestive issues currently, and he probably needs to be seen for them, but I don’t know how to take this dog to the vet anymore without making this reactivity worse. It seems the more we try, the worse he gets.