Been there, it's pretty good, don't know about the sauce recipe but it was definitely unique.
Here's some photos from my blog-
This is on 322 next to the Wawa. The Black & White milkshake was great.
I tried to find the other "John's Doggie Shop" in Chichester and couldn't locate it. It's definitely in a not-terrific area but i'd love to hear if anybody's been there. There's a video that makes it look pretty good. Search "John's Doggie Shop Chester" on youtube.
If you're in that area check out Jimmy John's Piping Hot Sandwiches as well, their natural casing "special frankfurters" are some of the best in the Philadelphia area.