Use a sealed NiCD battery from Dick smith $45- these do not leak acid.. about a 6 amp hour is enough for a few trips - this is an easy installation - just get some outdoor gutter silicond sealant and mount the transducer directly under the front seat, on the hull - squeeze silicone on the hull, just to the right of the main support beam and press the transducer into the silicone until it touches the bottom of the deck, use spit on your finger to press the silicone into a decent shape and make sure it seals all the way round the base of the transducer - align the transducer to point straight down, especially if you have a V hull -  the storage area under the front of the boat will hold the battery and make sure you put it in a lunchbox or something to prevet the terminals touching the boat - mount the display any where you choose on the front, preferbly centre, so you can see it from anywhere, and connect the wires - tip here - mount the transducer the night before you do the rest of the stuff and let it dry overnight before you start pulling on the wires. Run the wires out of harms way on the floor and cover with the rest of the silicone... simply charge the battery every few trips on the battery charger in the garage.

Good luck

I can take a few pics of mine if you like, and BCF has some cool portable lights for tinny's on special at the moment.. pm me if you need more advice mate

 a Lowrance Elite-5 DSI   GPS combo.Got one on my tinnie 4.6 Quinnie for up north and close in stuff. It will cost you about $550 to $600 on line [ebay] The down scan works great in shallowish water up to 30m. Cheers

I have the elite5 on my 4m tinnie have a motorbike battery(sealed) and store it under the floor between the front seat and the nose section. Works a treat!

Have seperate units on my 420 dory, built on a little console. Fitted it out for the units to be interchangable with bigger boat. 7in GPS and 5in sounder flush mounted. In my case if i was buying new and in retrospect a 7in combo would've been so much more a better option for visability and would take up much less space. Have a 100 cca marine battery that is the second battery off the other boat, $80 for a rectifier on the motor always keeps the battery charged and runs with 13v. Not sure about the busta's but the dory's have i groove in the gunwhale for all the wiring to run through. Didn't like the idea of drilling into the hull for the tranny, probably no more than $50 bucks to get you a ally bracket welded on.

pics and some tips from others in glastronics thread a while back http://fishwrecked.com/forum/what-modifications-did-you-do-your-fishing-dinghy-make-it-work-you

In my old 410 Salmon(that my brother now owns in the N.T) i put in a Lowrance HDS-5 as the sounder. I used to take it out off W.A in water 50-60m deep and so needed something that was going to show me the bottom pretty well. Works pretty good in shallow too. On a recent trip to the N.T with my brother we could easily see Barra and even Crocs on the sounder if we drove over them, mostly in water 1-12m in the Rivers up there. Had that wired to a Marine Battery that was also charged off the 40 Mariner 4stk on the back(electric start and power tilt), so never had to worry about pulling it out and charging it. Battery location was at the rear opposite the fuel tank. Couldnt be bothered with all the extra wiring to get the battery up the front, though for weight distribution it would have been beter.

For GPS i just used my old Magellen Explorist 100 handheld, and my brother now uses his Garmin Handheld. Couldnt justify having a plotter in the tinnie as most the places i fished down here were straight point A to B with no hazards inbetween. And in the Rivers up north it was more about marking danger areas(sandbars, rocks, snags) to let you know when you are approaching and to look out. Especially when starting the drive down river before sunrise!.