I don't believe that Nissan made the Frontier in 1991, so I'm going to assume that you have a 2001, with the large tubular crossbars. This rack should fit just fine. Thule includes 2 different length bolts in the box, and says that for some larger factory bars you may need to purchase longer bolts. If this is necessary it would be only a few bucks from a hardware store. The Nissan tubular bars are really any wider that most other factory bars, they are just higher, and that is why you need the longer bolts. Always remember to check the Thule configurator at the top of this page to check your vehicle for sure. This is a great rack (I personally own one) but my concern would be how far apart you can get the crossbars on your Frontier. How far apart they need to be depends on the length of your boat, but the further the better.