DON'T put any salt, borax or glycerin on a skin you plan to sell or trade. Us bow makers want them air dried, period. The don't stick very well to a bows limb if anything has been put on the skin.
I use a staple gun to tack them to a board and handle them like Shedrock does.
Copperheads don't need to be fleshed but big rattlers have a lot of meat that will need to be scraped off with a spoon.
After a few days of drying I cut the skin off the board, trim the belly scales off with a pair of scissors and store the skin in a zip lock bag.
If you don't have time to dry a skin you can roll it up, put it in a zip lock bag, fill the bag with water and throw it in the freezer. This bag has 4 huge timber rattlers in it that I haven't had a need to dry and use yet. They have been frozen for about 5 years.
Bowmakers seldom use one skin to cover a bows limbs preferring matches sets in most cases. A skin needs to have around 30" of usable material in it to make a good backing for bows. On bows with shorter limbs you can get by with 25" in some cases but that would be about the minimum.
Very big diamond back rattlers have too big a pattern to look right on a bow. Anything less than 50" would be OK.
Timber rattlers can be any size because they have three patterns on them. You can use matched pairs or split one skin down the middle and use the side patterns on each limb. I prefer to use one timber rattler skin split down the middle on bows. This is much better than wasting so much of two good skins to use the middle pattern.