SL vs SD vs QB vs..... What do they mean?

[Meteor]

Hi folks,

Sorry if this is already posted somewhere, but I can't find it. What do the letter designations in the model designations mean? I'm specifically interested in the 2720 & 2619 models, but I want the 2720 with a queen bed in the back, a double bed in the front, and a dinette in front of the front bed. What would the model designation for that be, and what do the letters in the model designations stand for? I thought they indicated the floor plan, but I can't find a 'key' to them.

Thanks
Meteor