I went to an informal one at a contest once. It was taught by Harry Soo of Slap Yo Daddy, who had been on BBQ Pitmasters.
I learned a lot seeing how he does things. The guy is a master of details on them.
I am not sure if there any specific places to go for a regular type of class though or if some regular bbq classes teach them. Maybe you could find something online.
I know there are some people on here that have posted pics of their boxes before so you might be able to find some more help here as well.