Its a very small trade so I'm not surprised by the lack of response. Being a small trade has institutional implications (think dead man's shoes).
Seamen become Navigators once qualified to Class 1 (I think).
You get to wear blue JHWs, shirts and trousers and the Army ensign on your arm (Seamen are known as 'bluejobs' for that reason).
They spend much of their career manning the RCLs (Ramped Craft Lighter), Workboats and Mexiflotes which are based out of Marchwood and some other locations (Akrotiri springs to mind). RCLs are commanded by SSGts (I think).
The RFAs new 4 x LSD(A)s take workboats and Mexiflotes. So, whenever they go to sea, chances are that a slack handfull of RLC Seamen go with.
Speak to your recruitment office or arrange a visit to Marchwood. PM me if you're getting nowhere.