Chances are, that an asphalt fence paint would have worked nearly as well, and had less environmental impact. At 16 bucks per 5 gallons, it isn't too bad a deal.
<font color=red>I have a 16 foot flatbed and in our Texas heat I couldn't keep anything on it--paint, Thompson's Water Seal (BIG waste of money), etc. My blacksmith friend suggested using waste oil, so I took some used 10W-30 Mobil 1, thinned it down a little with diesel fuel, and painted it on with a big brush. Boy, did it soak in! I gave it four coats before it stopped disappearing. Then I wiped off the excess and let the trailer sit some before using. Using a brush eliminated any runoff. The trailer bed has stood up well now for a couple of years. I plan to coat it periodically. When I used my trailer to help haul books for a book sale, I did have to stand and listen to an old geezer lecture me about the risks of cancer, but I couldn't help thinking of mechanics who spent most of their lives working with oil and grease and still live to ripe old ages. He was right, of course, in theory, but for as often as I use
<font color=black>If the trailer is left out in the rain, I can almost guarantee that runnoff will contain trace amounts of petro contaminants. Between the leeching and runoff, I would imagine that if you tested the soil under the trailer, there would be detectable amounts of contaminants.
<font color=red>my trailer, the risk is minimal. I really don't think that using my trailer is hazardous to the environment.