Thinking of buying new or used?

In 1984, I purchased a new Rockwood pop-up. The first thing I did was to buy cans of automotive undercoating and sprayed the entire underneath of the trailer. When I sold the trailer 21 years later in 2005, there was not one spot of rust on the frame of the trailer. In 2007, I purchased new Jayco Jayflight and did the same exact thing. Unfortunately my current Jayco Eagle has the cold weather package and everything is covered underneath, except the outer edges of the frame. Just before this past winter I went around the entire trailer with a can of black Rustoleum and brush. I painted every exposed part of the frame, rear bumper and from frame. Small amount of work to prolong the life of my TT.