There are a few places in the world where
living aboard is inherently so much cheaper than any possible land accomodation, that it is worth it for economic reasons. I think London may be one of those places; some people live in narrowboats in charming spots and pay much less than they could ever rent an apartment for.
But in most places it is not a good deal in purely financial terms unless you are willing to live at
anchor with no walk-on access, or on a
mooring ball, which turns into a bit of a hermit's life since you have to get into your
dinghy and take a boat trip to get to civilization.
Where my boat lives, for example, a walk-on marina slip is about $20,000 a year -- a sum which would get you a perfectly decent apartment, probably even one with a
water view. And the slip fee does not include the cost of the boat and her upkeep.
So I'm not sure living aboard is such a good idea purely as a residential strategy. It makes much more sense if you are doing it just to be on your boat more -- because you love your boat and love the water so much you just don't ever want to be on land if you can help it.
I
live aboard about 90 days a year, either cruising or on my mid-river
mooring with no walk-on access. For a couple of months in the
depth of
winter, in a marina on the Isle of Wight (walk on, but a
ferry ride away from civilization). I do it because I love my boat and want to be on her as much as possible (plus I have an endless list of things to
repair or improve or clean or maintain).
As to the practical aspects of living aboard:
Condensation and
mold, which you asked about, is one of the inherent problems of living aboard. The only solutions are lots of ventilation, keeping matresses and
cushions blocked up for air circulation, and cabinets open (or with built in ventilation like mine) when you're not on board. My boat has six large dorades -- that's a hot tip for ventilation. A cored
hull is also very good for this problem. Four of five days away from the boat is not a problem. I leave my boat to her own devices for a month at a time, sometimes longer. I always worry about her, but she seems to do fine on her own for such periods of time.
A houseboat on pontoons will definitely be better from a condensation point of view. But what can you do with a pontoon boat? Why would you want one? Sailboats can sail, and sailing is actually quite a lot of fun. Boats are made to take you from place to place -- this is another hot tip for the prospective
liveaboard.
Another thing to say about living aboard is that a typical
liveaboard sailboat is going to be quite a lot less space than what you are used to living in on land. You will have to lose about 90% of your possessions, on average, if you want to live full time on a boat, unless it is a very big one. Does it suit you to live in a really small space? My boat, 54 feet and relatively new, is relatively large and luxurious, for a sailboat. But I would go crazy living aboard her if I were not moving around regularly. Especially on a mooring where it requires some effort to get ashore, you are pretty cooped up with no place to walk around, limited number of places to sit, etc. This is not a problem when you move at least every week or so, exploring new places and so forth, but staying in one place it would not
work for me.
Another aspect of living aboard a boat is that the engineering systems are rarely as convenient or functional as what you will be used to on land. For
cooking, you will have to hump gas bottles, and you will have to take
safety precautions which are somewhat tedious on a day to day basis. You will have a big problem with water if you are not on a walk-on pontoon with a water tap -- you will have to use it sparingly and have some way to fill up every week or so.
Electrical power is not such a problem in a marina, but on a mooring or at anchor you will have to produce and store it -- even with a built-in
generator, this requires a fair amount of management.
So if you just want to live somewhere, I can't imagine that you wouldn't be better off with a
cheap studio apartment somewhere. If on the other hand, you crave to be on the water, like most of us here, and/or love to sail, then it's an entirely different story.