Re: Best method for adding covers?
You can buy covers at dozens of places. SD sells them as well. You can spend $20 per to $100 per. SD standard spacing is 49.2mm, so don't buy 50mm or even wider covers.
As far as installation, I've always used a strip of plain ole masking/painters tape, just wide and long enough to cover the slug coil. Then raise the pole pieces so they'll go through the cover. Press it on firmly until the poles are through and it wont go any farther. You can use a clamp to hold it tightly in place while you tac the two solder joints.... then you're good to go. Sometimes there is a satisfying snap when you put a cover on, other times you get no snap. The main point is get it on as tightly as possible.
After you do it once you'll get it. And you can always cut the solder joint and try again if needed. You're trying to make sure there is no air gap between the cover and the slug coil. Plenty of guys will say the tape is not necessary, but it works for me and my covered pickups don't squeal.