Seabass - Yes if you epoxy into the hull the temp sensor in the transducer will not read water temp, so you have a couple of choices (and I know Greg from Humminbird will give you even better suggestions) would be to 1) epoxy into the bildge and get get the approx $20USD tempature sensor to mount on the transom (here is a link at Amazon - http://www.amazon.com/Humminbird-7300101-TG-Temperature-Sensor/dp/B000FIF6Y2), or 2) mount it on the transom like it was meant to be, i've mounted a number of transducers over the years on my 700lx, all have been Humminbirds so with 1 exception i've not had to drill anymore, just used the same mounting hardware. The 1 exception was the SI unit's big transducer which needed to be mounted higher up the transom so I epoxyed an old transom transducer into the bildge so i'd be able to keep bottom while on plane and used a Y cable. the other option is you think over the years you might swap transducers and companies, is to mount a seperate plastic board once to the transom (still gotta drill) and then you have a seperate mounting board to attach your transducers to (read about in an issue of Trailerboats mag years ago). When you drill remember to tape the area (to ensure no clearcoat cracks) start spinning the drill backwards to get it into the fiberglass, and after drilling and before using the screw use Marine Epoxy in the hole to ensure water tightness.
Trep
It makes me so proud! 
