Recently purchased an Avenger 27BBS which has a 15 ft. slide out. I am wanting to order a Dometic Topper for the slide out and I am getting conflicting information on ordering the correct size. I called customer service at Dometic and I asked the lady if I order the length of the topper by the length of the slide or should there be any overhang. She said for the 15 ftl slide order a 180 in. topper. Instructions upon ordering from Camping World says "measure exact lenght of slideout, add 6" and if necessary round to next highest 1/2 ft. This seems to be some of the typical conflicting info I tend to get from the distributers and the manufacturerers. So I come to the more knowledgable folks in the RV world, the owners on a RV forum. I'm have about decided to leave it bare and sweep it off before retracting, but what are your experiences in proper sizing for toppers? Thanks for any input!!