To add a couple of points to Sally's great instructions:
It's best from the point of view of the skins to take your lambs for slaughter slightly later in the year, say October, but no later than November, as the wool will come off. But in October we often have very dry, very cold air (here anyway) and that helps with keeping the skin from rotting, and speeds up the salting process. If the atmosphere is damp ie high humidity, then the salt will absorb the atmospheric moisture when it's supposed to be sucking it out of the skin. I find that if it is humid, then roughly covering the skins with polythene will help.
Wear rubber gloves and a waterproof apron when you are doing the salting - it's a horrible job
We wrap the salted skins in plastic feed sacks for transport. If you have salted them enough then there shouldn't be much of a problem with leaking, but it wouldn't be very nice for everyone else's parcels if there was