a space is usually required so that air can circulate and really cold air isn't trapped, i.e. making the bubble wrap next to useless, so personally I think the spacers are best - but it really depends on whether and why you really need to insulate further - a good idea is a min/max thermometer and be ready to fleece anything that really needs it by watching the weather forecast
they've got to be the longest urls I've ever seen, my screen stretched into next week ;D