Just a couple of points to add.
It is my experience that you do not want to have the back anchor attached to bungy only as this allows far to much potential movement of the boat if there is a swell and you can end up with the boat on the rocks
Generally a 10m length of bunny attached to the anchor chain and then to a rope is enough to give you the ability to pull the inflatable back to the rocks through out the full range of the tide.
The other point that works well in challenging conditions/spots is not having an anchor on the front rope. It is easier to throw a rope already tied off at the front of the boat on to the rocks first then have the front person get onto the rocks and grab the rope and let the rope out as the boat person positions for the boat for the back anchor to be set.