I had not quite 4 year old tires on the fiver I recently bought, first trip out with it, blow out going to destination and another coming home. Was in the motor home thinking mode, 5 yrs as approx....had good tires for another year or two. Wrong. 3 tire places told me 3 to 4 year for trailer tires
Replaced all 4 before next trip and upgraded the load range.
Better safe than sorry. My tires looked almost new, were inflated correctly and sure I was not overloaded. Not fun sitting on side of Interstate, by myself with my pup. Good Sam did an excellent job for me both times.
My advice, after my experience...get new tires before you leave.