Unless you clearcoat a painted pinstripe with a UV protective product the paint will breakdown over time and fade. You will see the fading first in the sweeping curves of the pinstripe because when rounding a corner the striper will be putting on less paint in the curve. You can get around this by taping off the stripe and rolling it in, but the edges are not as clean. The best way is to lightly sand the tins, apply stripe and then clearcoat overtop. A hand applied pinstripe will last a few years at least before you notice any fading.