hope this helps someone from what could have been a really bad situation.
Friday night I was leaving for the lake, when I pulled out of the driveway (gravel) no problem when I got to the main road the trailer locked up. felt like the brakes were frozen. I got out and did a quick visual check and couldn't find anything wrong. backed up with little or no resistance which is odd that should have engaged the brakes. forward still the same. thought maybe a piece of gravel had lodged in the brakes. repeated the forward backward a couple of times and it came free so back to the drive way for a full check. pulled the wheels to discover the pass side caliper was no longer mounted. just bouncing around inside the wheel. both caliper bolts were gone, only the brake line was still holding on. not broken GONE! long story short I ended up replacing all of them on both sides and off to the lake by midnight. one more item for my annual checklist.