I know this is an old thread, but we recently discovered a problem we've had since we bought our 2007 WW FSC2800, new, in late 2006.
The 2007 is a tandem axle Toyhauler; for the 2008 model year they went to a triple axle. That should have been a tip-off. We opted for the cleaner-looking fiberglass body (as opposed to the corrugated aluminum, which is MUCH lighter).
Almost from the start, we were experiencing blown tires on almost every trip; sometimes we'd blow two on the same trip. The tires were properly inflated, and checked at every food, rest, or fuel stop. We tried numerous brands of tires - Carlyle, Firestone, and Goodyear. Same problem with each - we'd be rolling along at 65mpg, and "POP" - a tire would blow. Sometimes the tread de-laminated from the carcass; other times, it just blew out the sidewall & shredded as we pulled to a stop. Once, it destroyed the fiberglass tire skirt, and took out the rear running lights (it was nighttime, of course).
The trailer's weight (according to the CAT scale readings when it was new) was well within the GVWR specified, and we always tried to balance the load evenly, so we didn't suspect a weight problem.
To say that this issue diminished our enjoyment of the trailer is a gross understatement; in fact, we rarely used it because of this.
Finally (just recently) we re-weighed the trailer, empty (~9400 lbs - very close to the original numbers we got). The weight we were hauling seemed to be within limits, even with 150 gallons of water, and a full Generator fuel tank and two bikes loaded.
I thought the wheels looked "skewed" - or out of alignment, so I took the trailer to a truck center that did Laser-alignment (I thought one or both axles was bent).
The good news: the axles were fine. The not-so good news - 3 of the 4 wheels were bent. Now, with all the tire changes we've had done (which required balancing), not a SINGLE shop indicated that we had bent wheels. The truck shop also informed us that they thought we were overloading the tires. We hadn't even considered that.
The tires on the trailer were 15", load range "D", rated for 2600 lbs EACH (for a total of 10,400 lbs. That's only 1000 lbs more than the empty weight; just filling the fresh water tank exceeds 10400 (150 gallons x 8.3 lbs = 1245 lbs, which put our gross weigh at 10,645, almost 250 lbs over the tire capacity! That's with nothing else loaded, and no fuel in the generator or fueling station tanks (let alone the contents of the black & gray tanks, toys, cargo, food, etc).
Last month, we installed 16" steel wheels & Carlisle load range "E" tires (mfgr p/n 5193411), rated at 3960 lbs each @ 95 PSI (for a total tire capacity of 15,840 BUT - the best 6-lug, 16" wheels available are only rated for 3200 lbs each @ 80 PSI (total of 12800 - which is about the GVWR of the trailer anyway, but less than the tires). To get higher capacity wheels, we'd have to change the axles & go to 8-lug hubs/wheels.
But still, we now have 2400 lbs more capacity than we had with the "D" range tires. In addition, the rating on the wheels is most likely conservative, so we probably have an additional 100-200 lbs per tire as a safety margin. We don't intend to push that limit, but still; it's nice to know it's there.
I hope this long-winded post is helpful; if you have a similar problem, check your tire load rating... if we had done it sooner we'd have saved LOTS of $$$ and headaches.
Tony