Gulf Stream's Amerilite has two 21' fifth wheels. One has a slide and the other does not. Their Conquest name has 23', 24', and 26' floorplans. Your truck, of course, can pull larger than this, but if you would like more information, let me know.
Why are you looking for 'the shortest'? With your truck you should be able to pull a bit more. We found a 24.5' to be fine for 2 people (and a flock of cats) for weeks at a time, but I wouldn't have wanted to go any smaller.