The thinner the paint the less deep the chip will be and water will not hold there. When metal is exposed, as in bonded or not, it will rust. The rust will go sideways and if the paint is brittle it will flake off to leave a dryable area but if plastic at all the water creeps underneath and stays there.. I've had my tow bar and bike carrier galvanised, not very pretty but indestructible. The dipping during the process even galvanises the insides of tubes.