I don't usually use preserving agents unless there is any flesh present and to be honest unless you really need the wings its alot simpler and quicker to chop them off and preserve them seperatly. Usually I throw the French partridge wings away.
How I do it is use the scissors cut off the legs at the knuckle and the wings at the elbow.
Use a sharp blade and make a small incision through the skin then using the scissors again point the lower blade through the incision and cut towards the beak right the way up and repeat the process down towards the rear.
Using your fingers open the skin like your taking off a jacket. On french, pheasant,snipe and such it's easy and comes off without any flesh attached but woodcock is a bu*ger the skin is like paper and you keep ripping it.At the head pull the skin as far up over the head and cut with the scissors.
When you come to peeling off at the wings there is 2 sinues attaching the flesh to the skin, one above and one below where you might need your scissors or scalpal just to cut to prevent the skin ripping.
When your this far the skin should be completly off the top half, next is to lay the the bird on its back and push the legs back through the skin, then a constant pull on the skin downwards will remove the skin at the tail with no flesh. On a bird where you want the tail you will have to cut the flesh and treat it.
On shot birds remove any blood from the skin.
Preserving
Lay the skin skin downwards on a news paper for 24-30 hours in a dry,warm environment then lift the skin and lay feather side downwards on a new newspaper for another 24 hrs and this should do it.
Killing mites
Freezer for a few days but ive started microwaving for a few seconds
Washing (optional)
I like to wash mine in detergent rinse then wash with conditioner
Sounds complicated but when you get the hang of it, it will take you literally 1 min to skin a bird.
Disclaimer
I am by no means a professional bird skinner guy, so the chances are someone could disagree with some of the above. I do recieve an enormous amount of game and the above works for me, ducks are alot more fiddley because of the fat attached to the skin.
I would welcome any better way of doing it.
Hope this helps