Fuel fill cap locks
 

Thinking this might be a good time to install one since the boat is slip kept during the season.

Can't find any that would replace the standard flush mount type. Who has them?

I just ordered a set from these folks. They're very high quality. You'll have to download the PDF of their catalog to see them. The locking cap is an option. The also have a stud mount that has no screw heads showing on the mounting flange. http://www.southco.com/product/class.aspx?cid=7581