Has anybody used the DIY bedcoating for a trailer or other large surface?
Mine is steel treadplate, but it is slippery when wet.
I saw on Power Nation where he put the Dupli-Color Kit on flat bed truck.  I like how it had chunks in it, that should definitely help with traction.
Is the Dupli-Color good and thick enough or is there a better option?

Anyway, there's a couple spots of rust coming through and I haven't gotten around to waxing it for the last 3-4 years (I did the first 2 or 3 years).
And I've been wanting to weld on a few more hooks and anchor points, so this would give me a chance to paint and protect those.

Fixing the rust would be my first priority.

After that, cut/weld in the new anchors.

Then I'd put some kind of bedliner with traction material in it.

All the DIY stuff I have seen usually turns out like crap.

I have used both Herculiner and the Duplicolor.
Both are better for protection than basic paint, but no where near the protection that an actual spray on like Line X etc. will offer.
Also, regardless of what Herculiner and Duplicolor may claim, their products aren't UV resistant.  If you don't want them to fade, you have to top coat them.

My trailer is wood floored, with a two foot dovetail in steel diamond plate. I used the Dupli-color spray on the dovetail. It works well and has been there for two years. It fades compared to the rest of the black paint on the trailer, but it gets cars and other shit dragged across it pretty regularly.

Best of all, I don't slip and bust my ass when it's wet.

Yep.   It winds up peeling off with any hard use.  

DIY bedliner works great for trim,  rockers,  and other paint projects where a rust resistant,  durable coating is needed.   It sucks for truck beds that see any real use.

This trailer doesn't see hard use.  It sits out in the weather all the time.
When we haul something not on wheels, we put down truck bed mats or plywood to prevent scratching and gouging.

So the coating would be mostly for corrosion protection and traction when wet.