When this happened, did the leaf springs splay at all on either axle? If so, you may want to realign them and get the leafs strapped fore and aft of the axle. When they splay, they don't load up consecutively and then spring fatigue occurs. Usually the long leaf snaps right where the axle meets the spring and when the trailer is fully loaded. It's inexpensive to repair beforehand but can sure leave you stranded at the most inopportune time.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )