Back to the cover. I bought the stretchiest material available, despite the fact that it has an alarming level of shine. Mine is a glistening Lycra with a fantastic four-way stretch - the kind of thing that you could make a leotard or dance leggings from. This is better than a simple jersey as it clings to every curve and it actually goes in at the centre of the bust, rather than standing proud and creating an unattractive mono-bust. That's important. I bought half a metre and managed to make a cover for my failed mannequin and this one from it...but the fabric was very wide and I'm the same height as a twelve year old, so if you're taller you may wish to buy more. However, because it's meant to be skin-tight and this fabric can stretch so efficiently, you'll need far less than you think - I was amazed when I didn't need to return to the shop for more Lycra supplies after making a cover for the original now-at-the-recycling-centre mannequin.
The tube should be a really tight fit as you want the fabric to stay in place and not have loose wrinkles that could move around once you're actually working on it. I removed the finial from the top of my mannequin and put the tube on the mannequin wrong-way-out, with the seams showing. Using a chalk pencil, I drew on lines to mark out the shoulders and the sides of the neck and then across the top where her head stump sits. These lines should be precise - there's no need to add in any ease.
I removed the fabric tube and sewed directly on the lines I'd marked out and then trimmed away any excess material, notching the seam allowance on any sharp curves. Finally I turned it the right way out and put it on the mannequin. It was a perfect fit for very little effort - this really is an easy-peasy way to do it.
My mannequin has quite large adjustment gaps, but these are pretty much hidden (apart from at the horizontal shoulder seam where it sinks into the gap just a tiny bit more). It really does feel like a very usable, fully-stuffed mannequins as the stretch fabric is so taut across the gaps.
I hope that was informative - I'm guessing this is rather a niche post, so apologies to anyone who doesn't wish to cover a body-double in spangly Lycra...normal service will resume later in the week.