I agree with tuna man, anchor ball is the only way I'd do it. Coiling that much line is job enough....pulling the anchor from those depths yourself and coiling it would be nuts. I'd carry the line in a small plastic round bin, and have quick snaps at the ends of your anchor lengths for quick attachment or separation. More anchor line is good, I have not anchored on my boat in over 225ft of water, but I have 15ft of chain and a light anchor and anchored on a nasty 5-6ft stacked sloppy day. 20ft should be enough, also instead of increasing your anchor length, get heavier chain, that works just as well. You will need a 2:1 min and 3:1 ideally for most conditions to hold at anchor, anything less is asking for trouble. I'd carry 1200ft of line if it were my boat, 3 400' lengths. If you only need to sue 2, no need to attach the third, but if it is nasty, you can attach a third and be safe.