The fiberglass fenders on my Ameritrail trailer keep coming loose.It"s an aluminum tandem trailer that my Sterling came on.Not much problem with the bigger bolts that come through the trailer frame but it"s the small vertical screws.They come loose,tighten them up & they get loose again & this is with lock nuts.I talked to Scott at Ameritrail,said he has seen problems with this.He said I might try shims.Going on long trip in 2 weeks,pulling the boat.I might have to go back to stainless steel fenders but would like to get a permanent fix on this.Can anyone help,idea"s?