Looking for some tips on builing my own cargo trailer

[bluebombersfan]

I have a 6 by 10 foot utility trailer that want to convert into a cargo trailer. My question is this. I am using plywood all around and am wondering if using a good few coats of tremclad on the roof would be good enough to seal it against water. I know fiberglassing would be ideal but do you guys think 3 maybe 4 coats of tremclad do the trick? I have used tremclad on my plywood flooring in my boat and I have found that it seems to have good sealing capabilities. The only flaw I found was that the floor does take a lot of abuse causing scratches but since the roof wont have any sort of traffic/scratches I was thinking that it should work just fine.
What do you guys think?

 

[Turbroke]

If you store it covered up (even a tarp would be enough) it should be fine with any kind of exterior finish. I'm building one too, but want to keep it light and convertible so I can still use it as a utility trailer. I'm going with braced, corrugated plastic. (The stuff they make outdoor signs out of) It's cheap, super light, strong and weather proof. That may be a good choice for your roof. It even lets some light through.