Most boat owners are content with one pair of trailer guides, but for those with larger boats, it can be helpful to install a couple of pairs for a total of 4 guideposts. This is especially true when it comes to those large 25-foot and 30-foot pontoon boats. You should never need more than 4 posts, though, unless you’re towing an incredibly large yacht, but that’s a different subject.  If you do opt for a dual-pair setup, then it’s best to install a pair towards the rear crossbeam of your trailer and the other pair towards one of the central or front crossbeams to provide complete support.