I wish I never had a bad boat trailer experience but unfortunately I have several. Two of them have been on the upper Colorado River, once at the put in and the other at the take out. These are days that started great and ended terribly. If you grease your trailer bearings regularly you might not find yourself in one of these predicaments. My first encounter with blown bearings was after a TEVA games pre float down the Upper Colorado. We had a great group of guys and we were floating a section we thought my be in the fishing part of the contest. At the take out I hoped in my truck and noticed my trailer wheel viciously warbling back and forth. I pulled over an we analyzed the situation. Yup the bearings had seized and with no way to get the race off my axle we had to throw the boat on top of the truck to get it home. Several auto parts later we were able to fix the problem and get the trailer back from Radium. The second story is much like the first so I will spare you the details. But, when it comes to trailer bearings I have gotten an education the hard way. I would keep the following in your truck anytime you are towing a trailer.
Paper Towels/ Rags
These are the essentials you will need to change wheel bearings should you run into the event that they seize. You can tell when one goes as you are driving down the road. The trailer will jerk a little bit, just enough not to notice that something terrible has just happened. Also, if you touch your hubs and they are screaming hot. Time to make the switch.