[Newbie_spearo]

personally I'd rather put it in hot water, and maybe heat it up on a stove if you need to do it slowly? I'd be worried about the sun damaging the line and possibly making it brittle. I realise you're only doing it once but I'd still go with the boiling water approach.

Just my 2c worth, I'm not an experienced spearo, but I've played around with hot water and my floating float line.