Perhaps I should start a new thread but since we are all here already...
My General Radiotelephone Operators License covers me on the RRO correct? I will not need to take another test element to use a marine SSB?
Yes, that's correct. The GROL (PG) conveys all the operating privileges of the Marine Radio Operator Permit (MP) and, of course, the Restricted Radiotelephone Operator Permit (RR). It also permits you to "adjust, maintain, or internally repair" marine and aviation transmitters.
There are several other classes of marine operators permits. You can read all about them here (see left hand column): FCC: Wireless Telecommunications Bureau: Types of Licenses: General Radiotelephone