When making a cap with dc, I find that making a sl st to the beginning chain makes it a little "gappy," since the chain isn't as thick as a dc. I hate that gap, so basically I just ignore the beginning chain of each row. I ch3, then put the first dc back into the same stitch as the ch3. When I get to the end of the row, I sl st back into the first dc, not the chain. It is much easier to see where to join if you use the first dc and this eliminates the gap (without increasing the number of st in the row). You can still see a seam, but at least there are no gaps.