Gloss: Will it last longer with 2nd coat?

I'm painting a new gutter board, before I put it up. I've primed it, put 2 coats of undercoat on & a coat of gloss (Dulux Weathershield exterior gloss).
At the moment it's dead easy to paint. I'm wondering is whether it's worth putting an extra coat of gloss on now (while it's very easy to paint) to give it a longer life? If it's likely to mean another year or so before I have to paint it again, then it's probably well worth doing now.
Any thoughts?
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