A hairline crack had started before, except we didn't' catch it. You could see where it had been cracked, and rusted out a little. After it split all the way through on both sides (not sure when it happened exactly, but when we pulled into the campground there was a lot of bouncing of trailer, and when I looked at it, it was cracked through on both sides) The only thing holding the trailer together was the fiberglass shell. I think it happened the last mile or so going down a bumpy road because that's when I started to notice an extra bounce. Luckily it happened then, or who knows what could have happened. No other damage. This isn't' something to overly worry about, but it's something that every boler owner should check on periodically. I still check the frame before I tow it. It takes 15 seconds.