Remember the reasons that made you decide to go in the first place. I always ask myself why wouldn't I go to the gym.

I'm bisexual, if I can't get sex I buy it.

I'm not sure that a wood burner would introduce water vapour, you need to speak to the underlay manufacturer. Call their technical department and explain the build up.

If it was a normal cold roof attic you would need ro ventilate the loft space above the insulation to remove any moist air. If it's a summer house and you don't make any moisture you may be OK. It's the moisture from showers and dishwashers that xreate moisture In our houses, no so much an issue I outside buildings without steam in them, it might still be worth ventilation the space above the Insulation though, and try and make the ceiling air tight with a membrane.