Dave,
I use a 500 Attwood Tsunami bait pump on my boat (Glass)
Best I dea for you is to mount it out thru the transom and fit an elbo pointing down and cut off at an angle so as to pick up the water when moving.
Have installed several this way and it works well.
Any BLA stockist should be able to get you one.. if you have trouble I can get one for you.