To install bucked rivets you obviously have to get to the back side to hold the bucking bar. Many times that is not an easy option if the trailer in intact otherwise. If you only have a few to replace just use Olympic rivets and shave the heads (Steve has them at Vintage Trailer Supply). If you are going to use bucked rivets you need a good 3X rivet gun. Most aircraft supply houses have them, do not try to use an air impact hammer. Riveting is not hard but there is a learning curve. An old US Navy aircraft mechanic taught me. I would suggest lots of practice on scrap before trying to set any rivets on the skin of your trailer.
Again, it is not hard to do but takes some practice to get the feel of it. If you have a local airport find an older A&P mechanic, he will probably be glad to give you some tips. If you only have a few rivets, he might even help you.
Bruce & Rachel
68 Trade Wind
2001 Toyota Tundra