RE: "Giant Scale" boats?
Tony,
Your imagination is your only limitation. An carrier wouldn't be too ambitious depending on just how detailed you want to make it.
I think I'd give the trolling motor idea a 're-thinking' though. Lots of power if your model weighs a ton, but more power than you'd -ever- need for most R/C models. Got an old 'F4F' laying around? Fold the wings, put the pilot on the nose with a pair of oars (so my imagination isn't exactly the best).
Another thing to watch out for is 'un-sealed' batteries. The gasses they give off can really do a job on a model (acidic). They do make for good ballast though.
Whatever you decide, have fun. Post pictures!
- 'Doc