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I was reading an article on masking canopies this week David and the guy recommends protecting the canopy with what these guys refer to as 'Future', but is called 'One Go', Pledge liquid floor polish. When it is dry (I give it a day) mask the canopy and give it another coat of 'One Go'. This helps to seal the edges and prevent under seeping of the paint. I say all this with tongue in cheek as I'm trying it for the first time on my two current GB builds.