Also, for the velux gaps I used Toupret Flex Fill (or Fill Flex) from a tube/caulking gun as it was a long thin fill. That stuff needs to be smoothed down when you apply it because it doesn't set hard (funnily enough, being called "flex"). But as a result should be less inclined to crack and has fibres in it for more anti-crack goodness. Used it around the built in wardrobe trims too.
Also, for the velux gaps I used Toupret Flex Fill (or Fill Flex) from a tube/caulking gun as it was a long thin fill. That stuff needs to be smoothed down when you apply it because it doesn't set hard (funnily enough, being called "flex"). But as a result should be less inclined to crack and has fibres in it for more anti-crack goodness. Used it around the built in wardrobe trims too.