As others have noted, the weights add up. A little here, a little there. Some of the areas where the differences can be:
1. One manufacturer is more accurate on the weights leaving the factory. IE: Some trailers have a few options installed, after the weight sticker has been put on it. Some have more options installed by the dealers, thus shipping weight on the trailer is lower. It's possible, they'll weigh pretty much the same, when leaving the dealer lot.
2. Different building materials. Wood / aluminum in various places.
3. Different options installed.
4. Different sized wheels and tires.
5. Different materials used in cabinetry.
6. Different sized propane tanks.
7. Different sized holding tanks.
8. Different "R" value insulation.
9. Underbelly enclosed / or not.
10. Different frame structure. IE: "I" beam vs "C" Channel vs Tubular, along with thickness of the steel.
All added up, one could easily weigh 1500 lbs more than the other.
