Proper tire pressure for the weight?

Our TM is a 2431KS. Bought it new in 2005, and of course it came with Goodyear Marathons. We had our first blowout when the original tires were 2 years old with about 18,000 miles on them, and we replaced all of them with new Marathons. Over Memorial day weekend this year we had another blowout, but again these “new” tires are 3 years old with at least 15,000 miles on them.

We’ve read the posts, stories and comments from others with tire issues, and understand that one school of thought is that under inflation is the principle cause of sudden failures. By the way, I’ve always made sure the pressure was 65 PSI cold before the start of every trip, and we never pull our TM with fresh, grey, or black water in any of the tanks. The “stuff” we carry in it doesn’t seem all that heavy, but until yesterday I had never weighed the loaded trailer.

Thinking that the load range D Marathons just weren’t man enough for the job, I bought and installed 3 brand new Maxxis M8008 ST load range E tires hoping that a heavier-duty tire might not blow out so readily. The Maxxis chart shows that these tires can handle almost 300 pounds of weight more than the Marathons, but at 80 PSI rather than 65. Fine, except that even at 65 PSI with the Marathons we noticed a lot of items inside the trailer were bounced and vibrated loose during each towing. Surely at 80 PSI the pounding would be even harder as the suspension on these TMs is not exactly cushy.

But then I weighed my fully-loaded TM.

Total axle weight the way we tow it: 3680 pounds
Driver’s side wheel: 1900 pounds
Passenger (door) side wheel: 1780 pounds

Why the difference? Well, we have removed the awning and its housing from the door side (it’s heavier than you think!), and the fridge (packed with food) and water heater (which we don’t usually drain) are on the opposite side.

But wait a minute – those Marathons were supposed to handle 2540 pounds at 65 PSI! We weren’t even close! Was I OVER-inflating them??

The Maxxis chart for the tires we NOW have shows that for 1900 pounds (the heavier side) we only need 40-45 PSI of pressure. That seems awfully low to me. Sure, the trailer won’t be as “bouncy” (my wife says “destructive”) at lower pressures, but I’d like some reassurance that 45 PSI is enough, and I’m not missing something obvious.