Owen,
I mounted mine on the outside at the bottom of the transom. It seems to
work ok but is not very protected except by the bottom back hull keel. I
put it in with wood SS screws and 3m marine sealer. I did read about the
interior mounting. Seems nice, easier to route wires, etc. but I didnt
have any experience with epoxy work, didnt have the epoxy, was unsure it
would work for me and didnt want to pay someone. Plus the manual said it
could reduce the accurate functioning of the unit. Plus in my Platinum it
had a rare for a fish finder, water wheel for the speed indicator and temp,
which had to be on the outside so I ran the wiring together on the
hull--had to do it anyway so did the transducer too.