Can i add something , do yourself a favour and add a small 6 mm high rounded lump on the inside of the boom before gripping. A V grip boom is the ants pants Those callouses in your avatar will be a thing of the past .
just need to paint on some markers for the harness. I tried fabric paint but it came straight off. Any ideas?
Go ahead and use it w/o marks, using your best guess which will be very close, then you have you harness line depressions in the grip to act as your marks, those don't go away.
Put a paint pen in your kit and once you've sailed you harness lines to the right spot draw a spot on the sail before you derig. You can mark your boom height on the luff too.