Hi Mate,
I'm certainly no expert on electronics, but I used to have a portable sounder.
It shouldn't be too hard - simply adapting the power lead to run from a 12v source with an inline fuse. This could be anything from car battery or small sealed battery (probably best suited to what you need), right down to AA's. I actually converted mine the other way - ie to run from a jump start pack instead of the 8 AA's housed in the unit. I bought a power cable for about $35 and put on a cig plug with a fuse on it. You could also use croc clips I suppose.
The transducer was connected to the transom by a big suction cup - it might be hard to get a hold of one of these, but some sort of removable mounting bracket might be the go.
Good luck,
Mike