For the most part the width varies by year.
1968 and earlier trailers were 7 1/2 feet wide. In 1969 a new body style was introduced and the trailers grew to 8 feet wide. In 1995 the first wide body 8 1/2 foot wide trailers were introduced, but I think it was only available on the 34' models. The rest of the product line went wide body in 1996. The 8 1/2 foot is the width of the currently produced trailers.These are all exterior measurements...
These are general guidelines. There are some models that are exceptions.