Tailer tire horror show.....

I have a triple axle boat trailer running 205 Goodyear Marathon tires. In the process of towing my boat home, I blew a tire. In trying to get to a repair shop, I blew another tire (same side). You say proper tire inflation is critical. I checked all the tires and inflated them to 50 psi the day before. When I purchased the boat, I blew two tires trying to get it home. Again, 205 Goodyear Marathon tires. I'm just not having much luck with these tires I guess.