Sorry to hear of the issues you are experiencing.
I think the key word to your problems are with the fact that the trailer was used.
Our first travel trailer was (well) used . . . and even though it was very old (1978 trailer purchased in 2000), the people we bought it from said everything worked . . . but of course, being newbies, we took their word for it!
Well . . . come to find out, the only things that worked in that trailer was the electric (ie.- we could plug things in and didn't blow anything up) and the furnace . . . which we only ever used once in the 12 years we owned it.
We called it our tent on wheels . . . and the other name I had for it (and was going to have it painted on the back like boat owners do) was 'Trailer Trash'.
The roof and all of the water and sewer tanks leaked like a sieve . . .
Heck . . . even the trailer brakes on it only worked when we didn't need brakes (ie.- going up hill) . . . but rolling down the other side of Wolf Creek Pass . . . NO BRAKES . . . AAAAAAAHHHHHHHHHHHHHHHH!!!!!!!!
But we learned to live with it and had a lot of fun with that old beast over the years.
In 2012, we purchased a brand new 2013 Heartland Trail Runner that brought us into the 21st century of camping and we loved it.
We had our share of issues with it . . . mostly minor stuff compared to what others around here have experienced with their RV's.
But two years into our Trail Runner and 1000 miles from home, we had major suspension issues!
We paid a large sum of change to get us through our vacation and then home . . . and then the real fun began!
To make a long story short, after finding out what was going on with this new trailer (despite being a year and half out of warranty), Heartland and Lippert (axle manufacturer) stepped up to the plate and not only replaced the parts, but upgraded them to the next level!
I did pay the labor charges plus all other associated charges to make the trailer better, but Heartland and Lippert did stand behind their products and provided the parts to make it right!
Now, it wasn't an easy road to get them to cover it out of warranty . . . but the key factor here is that we did purchase the Trail Runner brand new, so we were the original owners!
We had the Trail Runner fixed six weeks ago, but we decided to trade it in and upgrade to a new 2015 5th-wheeler . . .
But we did stay with the Heartland brand!
Footnote: Our Trail Runner didn't last a week on the dealers lot before it was sold.