the question is - why would we want to make a boat that floats there?
the temperature and pressure are WAY too extreme, you can't make a self-sustaining habitat on jupiter or any other of the gas giants due to the abscence of oxygen. the only reasons gas giants are handy is because they have alot of hydrogen up for grabs, the only thing to consider is transport.
a better proposition would be to colonize one of the gas giant's moons that have more oxygen. wether it is bonded or not. just a silicate rock planet or something, you can get oxygen out of sand with the right tools
to get the hydrogen up to the planet, you just make regular pick-up flights at the gas giants atmosphere.
and I think that we are not too far from being able to...
just think: there are already prototypes of ion engines that van travel very fast, so getting there and transporting stuff there won't be hard. also, we can break the escape velocity by using those engines, and those engines rely on helium ions, and since helium is around there plenty, the harvesting ships might be able to sustain themselves. if we can generate water and oxygen on the colonies, only food needs to be imported. energy is around in plenty too - fusion from the helium and hydrogen there.
the advantage is an almost unlimited supply of hydrogen and helium, and since helium is actually all you need to power ion engines, I think it's economically viable to use one of the gas giants as a hydrogen and helium mine. and we won't never even have to get to the liquid part of the damn gas giant. however, it would be interesting to throw in a reinforced ball of some sort of ultra strong material, with really thick walls and put somebody in it, and just drop it. I wonder if the ball could sustain the pressure so that the passenger lives when the ball hits the liquid ocean.