As you are learning the hard way, many (most?) trailers are not ready for prime time. With water tanks that you dare not fill and load capacities so low that you can't bring clean underwear, they are not travel trailers. Since you actually want to use the trailer, the only choice is to upgrade everything below the frame. Your other choice is to trade it for another product that may turn out to be nearly as useless.
It is doubtful that you will get all the upgrades, that are needed, under warranty. I did all the work myself after getting hosed much the same way as you. An RV dealer is not the place to get suspension work done if you are paying for it. If you cannot do the work, take it to a heavy duty truck/trailer repair facility and have real mechanics do the work.
As far as rough roads, you need to slow way down, these trailers will not take much abuse. If you need to gridlock the entire city, so be it, you are just trying to use the roads provided.
