Try going to PPL's website for their recent sales of MH. I did that when we bought ours in January and it was helpful. On the length of the MH if the seller gave you a model number that will help. Mine is listed as a 26Q and when I was comparing price I found that number, but the length was different on NADA. I would go with the closest to the number given. Remember he is probably listing all options on his and as a consumer don't list any.
2017 Grand Design Reflection 303 RLS
1997 GMC Sierra 3500 Dually