I use the alum/salt method and rub a little neatsfoot oil after drying and stretching. I suppose this will protect the skin from absorbing moisture, I have made rabbit skinned wrapped training dummies for the dogs and these get wet and dry out fine without any issues. The deer skins I have done don't get wet and I don't think it would do them any good, I think there are more permanent and durable leather tanning methods that would give you a water resistant skin out there. Best of luck.
Cheers for that pal, much appreciated.
Looking forward to getting cracking now, first stuff i ordered never came so had to order from someone else.