Hey Rory- from one gal to another- rowing a loaded boat in flatwater is a lot of work. Listen to these guys- they know what the hell they are talking about (most of the time anyway
Broke doesn't equal dumb. Don't go the kmart coffin route if you really want to do this trip. Beg, borrow or rent a decent boat for what you would have spent on the pool toy. You'll have less to worry about and more of a chance of really making this trip happen.
If there's anything that I can give you advice on- it's listen to your gut. If you're fighting every single step of the way to make the trip happen- then it wasn't meant to be. Quit fighting. If things work out- then go and have a great time. And put up some pics too!