My popup camper is about 13 feet from front of the body to the back, but longer if you include the rear spare tire and the front propane tank. I decided to go with the 14-16 foot length, which turned out to be just right to cover the tire and the tanks, and leave a little bit of material to also cover the tongue jack.
The top comes in a storage bag, and contains 5 straps, a handy throwing puck, and some repair patches. The top is labeled with front and rear tags, which makes it easy to put on. There are three straps that go under the camper, which is where the throwing puck comes in handy. You clip it to the strap and it provides weight to toss the strap under to the other side. The two longer straps hook together and are used to wrap and tighten the cover horizontally. Using all of these straps, I was able to cinch the cover down to my camper, covering all of the outside accessories. I did have to take care around the rear bumper, and ended up letting the cover ride over the top of it. Otherwise, the cover would have been pulled tight against the bumper corner and it would likely wear a hole in the cover over the winter. The straps that go under the camper are plenty long, as is the horizontal strap, and I had no issues cinching the cover down. The strap ends do touch the ground after I was done, so I had to tie them up so that rodents would not have an easy way to climb up. I'm sure they will still find a way, but at least I'm not rolling out the red carpet for them.
The camper is all closed up for the winter now, and I'm hoping this cover can last. It looks good so far, but winter wind and weather can really do a number on outdoor covers. I'll make an update next spring when we open it back up for the season!