Your first post posed the question, "How could the seals fail with only 400 miles on the trailer?"...
When you consider that it's about 800 miles from Pendleton, OR (where the trailer was built) to your location, the trailer already had at least that much "mileage" on it when you first looked at it. Then add your 400 additional miles and you're well over 1,000 miles when you had seal problems. The seals "should not have failed in 1,000 miles" but I wanted to point out that you're forgetting that "trip from the factory to the dealership"... That's a trip that has, for some owners, been a significant problem. From tires run with low air pressure to damage that wasn't seen on acceptance by the dealer (think towing on salt covered roads in January/February and the lack of cleaning the chassis upon arrival as one example)...
Granted, the seals should not have leaked. My guess is that someone at the dealership, during the PDI, did you a "favor" and used the EZ Lube feature to "give you something extra"... Seal failures are, at least in my experience, very rare on the "factory seals". Lippert doesn't "overlube" the bearings on assembly so there shouldn't be "too much grease in the hubs" and the chances of 4 seals on the same trailer being bad on the same trip are "calculatingly astronomical" so that leaves the "dealership as the most logical place".
It's good news that Keystone is agreeing to repair/replace the seals. At least you aren't faced with arguing about who's going to pay for it.... As for worry about your Yellowstone trip, seals are usually "extremely reliable" if not abused with the EZ Lube system. That said, anything mechanical is subject to failure, but all 4 seals at one time ??? There's a "common link to that kind of situation" and it's not the factory.
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS