Cunningham doesn't need to be very strong as loads are light to pull the main sailcloth tight.
I have a J hook with a block that hooks into the grommet on the main above the boom. One end ties off at another block attached to the mast boot 'eye', goes up to the J-hook block, back down through the block where the line starts and through a turning block on the cabintop hatch trim, back to a clutch.
See the attached pic for details.