Is there a sedative I can give to my GSD-mix during thunderstorms & fireworks?

My husband & I have a 10-year-old German Shepherd / Lab mix who is terrified of the sounds & vibrations during fireworks (going on now due to the holiday) and thunderstorms. He has always been this way. Symptoms are typical, from what I can tell: uncontrollable shaking, excessive panting & drooling, tries to access somewhere in our home that seems more insulated from the noise, etc.

When he was younger, we would give him a pill prescribed by our vet that was a sedative. However, a friend notified us a few years back that most sedatives do not actually calm the dog; they simply make it more difficult for him to express his anxiety that remains in full-effect in his mind. We asked the vet about this, and she confirmed that to be largely the case. So, from then on, we have simply tried to be calm with him, and let him self-soothe as much as possible until the fireworks / thunder stops or he falls asleep from exhaustion.

Fast-forward to now, and we're concerned he may harm himself due to his age. Is there anything we can give him on such occasions that will truly calm him, and not just make him appear more calm? If not, what is the best (mildest) sedative we can give him to make sure he doesn't go into cardiac arrest during one of these episodes?

Stats:
- 80-ish pounds, large & slender GSD build
- I give him daily: fish oil, senior dog multi-vitamins, and glucosamine supplements
- He lives indoors other than about 20-30 min of potty breaks, once in the a.m., once at night
- He is in fantastic health otherwise (knock on wood), and sees his vet once per year for a check-up
- We have 2 other dogs who (thankfully) are not bothered by thunder / fireworks, but who get anxious once he's in an "episode."
- He went though a basic training course at Petsmart when he was 1, and is generally very well-behaved and well-socialized
- We bought & tried the ThunderShirt on 3 occasions, but it didn't seem to help, so we've stopped using it

Any ideas are greatly appreciated! Thanks, XXXXX XXXXX Independence Day!

Optional Information:
Type of Animal: German Shepherd Dog
Pet's Gender: Male
Pet's Age: 10
Name of Dog: Boomer

Already Tried:
Other sedatives in the past, self-soothing, distraction, ThunderShirt.