If the behaviorist doesn't have it in her schedule to see you for several appoints then they are too overbooked to be effective to help you. You need someone who will do a consult, set up a plan, and follow up on a regular basis if you are going to make progress.
If Basil finds the gentle leader aversive then he may have started to make negative associations with touch. Also, leaning over a dog as most of us do to dress a dog in a coat is very invasive and can make some dogs respond in ways to get more distance. If Basil is good at impulse control and hand feeding, start making a requirement of feeding that your hand is on him for him to get his kibble. Start with your hand somewhere he is comfortable having it and as long as your hand is in contact with him he get to eat from the other hand. Then start to move you hand around his body. Watch for him taking the food with more force or pausing in taking food these are indications that he doesn't feel comfortable having that spot touched. You will need to work slowly on those spots to build positive associations by feeding while touching those spots.
If you have to dress him in a winter coat to take him out and it requires two hands then smear peanut butter or something equally thick and sticky on a clean part of the fridge so that he can lick it while you are dressing him. Human touching = food
If you are not already using NILIF, nothing in life is free, then start. He should be earning not only his food but also his other life rewards. If he wants to go out for a walk, then he sits and makes eye contact you open the door and release him to go out. If he wants to come sit with you then he sits and makes eye contact and waits to be asked up. Watch the video "Say Please By Sitting" http://drsophiayin.com/videos/SayPleaseBySitting.m4v