Just throwing some ideas out there, but have you ever tried an anxiety wrap on him? https://anxietywrap.com/default.aspx
(Thundershirt is another popular brand).
Also a D.A.P. (dog appeasing pheromone) diffuser or some calming flower essences might be useful for lowering his overall anxiety levels.
Regular, daily sessions of reward-based training could also help boost his self-confidence so that new things don't make him as nervous.