Peeling and chopping: I find this works best if I cut the watermelon in half (the long way) and then cut long, thin-ish slices of it. It's easier to skim off the dark green peel (and not take a lot of the rind, which you want for the pickles, with it) if you don't have to curve your knife out and around as you cut down. You also want to trim the flesh back. This time I left on perhaps a bit too much flesh. I wouldn't leave any more pink than this on the rind pieces, and would probably encourage you to leave less.
Brining (the salt water soak): Mix 1/4 c. salt for every quart of water, and just make as much as you need to be able to easily submerge your pickle pieces. I place mine in a large bowl (they just barely fit!) and cover with a plate, on which I placed a jar of brandied peaches, just to add a little weight and keep the watermelon pieces pushed under the brine (otherwise, they float to the top and do not get properly brined). Brine overnight or for about 8 hours in the refrigerator.
Pickling: When you're done brining, drain your rinds, rinse, and then cook for 5-10 minutes at a boil on the stove in fresh water. Then drain them again. In the meantime, make your pickle. Note: I made the standard pickle recipe (2 c. sugar, 1 1/2 c. vinegar, plus the spices - see my other post, linked above, for recipe and my notes/adjustments) and it barely made enough pickle to cover the rind I had from one medium-sized watermelon. You may need to increase the pickle if you are working with a lot of rind. Pour the hot pickle over your watermelon pieces and weight again. Pickle in the refrigerator for 8 hours. You can already see that the pieces are reduced in size by comparing this pre-pickling photo to the pre-brining one above. You won't end up with a lot of pickles here - unfortunately!
Cooking and canning: After 8 hours, pour rind and pickle into a pan and cook for 1 hour at a boil, checking often to make sure things aren't sticking. I usually cover my pan for the first half hour at least, so that the pickle doesn't cook off and I have syrup left to pack into the jars with the pickles. Can and process 10 minutes using the boiling water method.