I just bought a new to me trailer from a guy in Mesa AZ, and he also has a VERY well equipped 30' trailer for sale. Inside available box length as configured is 17'6". Sits in Mesa AZ. I was able to have my trailer delivered for $450 to Los Angeles. (I get nothing from the sale, just thought it was a pretty nice trailer.
https://phoenix.craigslist.org/evl/for/5967126378.html