The single most important thing when checking an aluminum skin, steel framed trailer is the frame. I rebuild and repair horse trailers for a living...well one of the hats I wear and although I think highly of the Trail et, I have had a few come to me with serious frame rot. I mean to the point that a horse could go through the floor and unless you have a trained eye...this may go unnoticed. Having aluminum skin tends to hide what goes on underneath and unfortunately the average horse person in my experience does not properly clean or maintain a trailer. Urine and manure becomes acidic and leaks down under the wooden floors. This corrodes the frame over time and if it gets bad enough the trailer is scrap or you will spend a fortune replacing the main frame rails. This actually involves removing the axles, fenders, and much of the aluminum skin in order to be done correctly. Aluminum skin/steel frame trailers are great...don't get me wrong and aluminum is not impervious to urine either...I have seen it eat through even aluminum floors. If manufacturers used a better coating on the frames in conjunction with educating owners on proper care, they would last forever. One last thing....cleaning the trailer with BLEACH is a HUGE mistake. No mater how much you rinse the trailer out bleach is a corrosive material and will find it's way between the floor boards and the frame. You are asking for trouble here. I understand the thought of disinfecting the trailer but at what cost. My choice is an anti bacterial soap loaded into my pressure washer feed and some liquid wax after made for pressure washers. Do this just twice a year besides all the regular clean out and you will be amazed. Just make sure you remove the rubber mats or the wax will create a skating rink!!!