Instead of applying sunscreen daily to your dome, why not just wear a hat or bandanna? Most of the guys I see working outside with shaved heads wear a hat; It is easier, cheaper, and more effective.
Also, you can always bring a "backup" bottle of sunblock in case you need it. They even make little ones that attach to your keyring.
If you do decide to wear a hat, make sure you still put sunscreen on your face, neck (back of neck too), and ears. I've seen quite a few guys in sunny Florida with skin cancer on their faces, necks and ears. Doesn't look fun.