Hello Ste,
not once have we used sleeping bags , we have one big double mattress topper and like I said previously two single duvets which are more than enough to cover both of us and more on the overlap , we use single duvets just in case we ever get lazy and decide to use the chairs as a single bed at the front !
In the winter we use a slightly thicker duvet as the same for the kids then in the summer a lighter one because you'll be surprised how warm it gets in the caravan . Some people think it's like sleeping in a fridge but normally I just go to bed in my shorts !!