If you are going to be in the business of designing and selling stuff that is dependent on knowledge of material properties and the use thereof, you should be able to back up your claims with something other than internet mythology.
Without defining any parameters, your claim of DOM tube being stronger than solid bar is highly flawed.
An example for you. Is 1" x .062 DOM tubing stronger than 1" solid bar of the same material? The answer is absolutely no, it is not. The internet is pulling forth the general rule of thumb that for the same weight of material, tube is generally stronger that solid bar but there again, within limited parameters.
If you decrease the wall thickness far enough, at some point it will not even be strong enough to support its own weight.
Basic example and comparison below. 1" x .120 wall tube compared to 1" round bar.
If you compare the two with an open mind and some critical thinking skills, it becomes evident as to how folks confuse basic material properties and then pervert that into a blatant falsehood. In the same materials of the same diameter, solid is always stronger. Unfortunately, that comes at a severe weight penalty. There is a 50% increase in load capacity but at a cost of nearly double the weight. 1.1 pounds per foot for the tube, 2.6 pounds per foot for the solid round.
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Ya'll aren't making springs out of tube because it is better, you are doing it because it is cheaper. There is a reason they don't make coil springs out of tube and your failures would have been far less if you understood why.
I have sent them an email to see if they are willing to stand behind their product and replace it. And will update this post when I hear back. 
