Aye Up Phil P,
Are you side-kick or what?! I'm just in the process of drawing up something that may be of interest to you.
But first of all are you aware of the previously Dutch Army issue (Brit pattern DPM) single hooped bivvy bag? I picked one up for about 45 quid about 18 months ago and it was easy to sew a piece of mosi net in at the zip, held in place with velcro. Hoop keeps the net away from the face - important otherwise the swine will just bite you through the net (that's why the net should be permetrhine'd too) and why a mosi head net has limited function as a sleeping option.
Second - I mod'd an ex Brit Army GTX bivvy bag some time back with a diagonal access zip and I intend to make a self supporting mosi net to go over the upper part.
I've got some net left over from a Brit Army mosi cot that I've adapted for a Lavvu upgrade, I will use a chunk of it for the bivvy bag upgrade.
I'm thinking of using 4 x 7mm glass fibre shock corded poles to form two small hoops to go to each side of the bag with one/possibly 2 further as a bridge between the two hoops (but I may end having to source some pre-curved ally versions to keep the arch size appropriate). I'll sew a couple of sleeves along the edge of the mosi net sides for the pole hoops. These and the bridge pole will keep the net (and the biters) away from me beneath. I'm thinking of attaching the lower end of the net to the bag with a strip of hook and loop and folding the upper end under the bag. If you've ever seen one of those spring-lock muslin type nets that are made to protect open food on plates it may end up looking something like that - but bigger.
Hope this gives you food for thought.