Catfish, kosher salt will work or sea salt, whichever you have or whichever you can get the cheapest(no table salt though). This process is easy...it just takes time. Sometimes it can take a month or two just to prep the skin and make the rinds. However, if you do enough skin, you can make enough for several years. You can usually get pork skin(back is the best) free at any butcher. If you are just getting the skin for fishing pork rinds, make sure you ask for this type. Otherwise, they will try and sell you pork skin used for rendering fat for soups, chowders, etc...Kind of like the difference in price between fresh bunker and frozen crabbing bunker.
What you need:
-Pork Skin
-You will need kosher or sea salt
-A few jars with air tight and water tight lids or anything that will not corrode and will hold the brine solution, is large enough to hold the skin you are using and can withstand boiling water
-A cutting board or old piece of wood you can cut on
-A sharp straight edge knife
-A really sharp razor knife
-Dye of your choice
First, coat and cover the skin in the salt and then roll it up. Both sides. You can't use too much salt.
Fill the container you are using with water and start adding salt. You want to keep adding salt, until you can't get anymore to dissolve. You should be able to tell when you have enough when the salt starts falling out of solution. This is ok, if it falls out. You really can't have too much salt!
Place the rolled up skin in the jar and leave it for 2 weeks or so. Room temperature or cooler is better. You don't want the brine and skin to get too hot or it will start cooking the skin before it cures it.
After 2 weeks has passed the fat and other tissue on the underside of the skin should have dissolved. You want to take the skin out rinse it in cold water. Now put it on a cutting board and take a sharp straight edged knife and scrape any of the remaining fat and tissue on the underside of the skin. The dissolved fat and tissue should come of pretty easily since the brine has dissolved, loosened or softened most of the tissue. You want to scrape until you can't scrape it any more. Rinse the skin again and cover it with salt again and roll it up. Discard the old brine and make a new brine solution to put the skin back in. Leave it for 2 weeks or so again.
You may have to repeat this process several more times, until you are down to just skin. The skin will turn white, almost translucent like a squid strip. When you reach this point you are done prepping the skin. Now you can cut pieces to your desired length, size, shape, etc...Best way to cut the skin is on a cutting board or old piece of wood with a razor knife. You can color the pieces of skin with food dye, clothing dye, etc...
I used to use a few different types of dye. Tintex or Rit work well. Tintex seems to hold it's color the best. Their are also food dyes that you can buy by the gallon that work really well. I can't remember the name of the food dye I used to use, but any brand food dye that can be done cold, will work. The best method was cold dying. Boiling the rinds now after you have prepped them will make them soft again and they can even curl up on you. When you dye, make sure you add salt to the solution. Boil water and then pour it in the container. Add salt again until it will not dissolve any longer. Then add the dye to this mixture and let it cool so that it is barely warm, tepid. Add the rinds and cover. Check them daily to see how the color is taking and when the color is where you want it remove the rinds. You can rinse them in cold water again to get any excess off or just put them into a container of brine. You may need to change the brine once more so that any excess dye is rinsed away. You don't want to get this dye on anything of value...it won't come off.
You can store the rinds in smaller containers of the same brine. Try and keep them out of high temperatures and direct sunlight or they will go bad on you. If you spill the container accidentally while fishing, just use some ocean or bay water until you get home. The seawater will keep them good for a couple of days. If your white rinds discolor or you want to remove coloring from your dyed rinds, you can add some peroxide into the storing solution. You can also redye rinds that have lost their color.
You can make a rind for less than 5 cents or so if you do a large enough batch. This more than pays for itself, since Uncle Josh's go for $5 or so per container of 5. It is certainly worth it, doesn't take more than a couple of hours max and when you lose a trailer, you don't have to curse as much
. You can also customize them to your size, shape, color, etc...I have used my rinds on bucktails for fluke and bass, jigs for sweet water fishing, eel skin plugs and swapped the eel skin for the rind...the uses can go as far as your imagination will take it.
I have also tried other methods, boiling the skin, rendering the fat out in a frying pan, etc...anytime HEAT was involved it changed the way the rinds turned out in the end.
Good Luck!