First of all you don't want your dog geeked on acepromazine. With the frequency of thunderstorms here I would not advize giving ace every other week. Personally I would suggest you try behavior extinction first. One of the primary stimulus that triggers dogs negative reaction to T-storms is the overpowering rumble of thunder. Most dogs don't like noise, combined as a audio-sensatory trigger, the stimulus is 100% terrifying for them.

The way to overcome this: download some thunder mp3 bits. Hook up your stereo and turn the subs all the way up. Slowly raise the vol until the dog reacts, as soon as he does have him sit, stay near and praise him. Distract the dog to focus on the commands and praise him as you continually raise the volume. If the exercise becomes to much for him, take a 30min break or pick up the next day. Increase the volume from sessions to session and continually treat/praise.

I did this with my current dog and it worked about 80%. During helacious storms he still reacts, but in that case I'm not usually sleeping either. In this case I usually lock him in a bathroom and turn a stereo up, it seems to help a bit.

Try these two things before medication, if all else fails medicate. But go ahead and discard the homeopathic plugins. Their success rate is less than the placeebo in double blind studies. (plugin type, some homeopathic oral drugs are passable)