I agree with the boats theory... a Landing Craft or something small, there should definately be a river or two on these islands, like Bronco said, and a few bridges (destroyable) every so often.
I'd like a cargo plane, like the C130 in the game, And i dont think it's a stupid idea, you could fit about 4 squads into one of those, imagine paradropping 48 men onto a position!?... sweet.
And I dont think it's possible to transport vehicles inside vehicles on this game, they just bounce around.