I am considering purchasing a 2000 like-new Flagstaff Model 176SDLTD pop-up camper. Unfortunately, NADA does not list this model in its price guide so I don't know whether the asking price is reasonable ($3250). The NADA guide lists the 176LTD (avg retail $1725) but not one with an "SD" in it. Does anyone know what features the "SD" model includes that are not in the LTD?