Auto Upholstery Summer Camp For what it's worth: A number of years ago I attended a week-long summer class at McPherson College in Kansas. If you all aren't familiar with the school, they are the only (or perhaps very few) schools in the country which offer a 4 -year degreed auto restoration course. One of the blocks in the course is focused on trimming.
In addition to the 4-year program they also do summer classes in a variety of subjects from upholstery, to metal work, to body and paint, engine building, etc... I had a really positive experience there and would certainly recommend it for others interested in these types of learning opportunities. These classes are suitable for teens, adults, you name it.