Hi Tony,
Please see my pics, just fitted a Railblaza rod holder and a pair of Quickfist rubber cylinder holders ( from Forces chandlers website) to hold a JLB Charge 4 (Currys)
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Make sure to use A4 marine grade bolts with penny washers on the back and locking nuts
Marine Bolts & Screws | Boat Fittings
These still leave room for mirrors if you wished and save a fortune. Just remember a blob of marine grade silicone both sides of the bolt holes, fit in a good solid area of plastic and don't leave too much bolt thread at the rear to sure you can still seat the top correctly.
Couldn't think of a better way than this without spending a silly and unnecessary amount of money.
Hope this helps.
Paul