PVA does absorb moisture like you wouldn't believe. You may have bought PVA from home depot or somewhere like that before, to use as a glue or to water it down and paint with it and use it like a sealant. If you've ever done that then you'll know just how water soluble this stuff is, which is kind of a big clue as to why this stuff so readily takes up moisture. Anything that's water soluble will do that.

I found that I had much more success when printing with HIPS for dissolvable supports, but there are a few things you should be aware of. Firstly Limonene, which whilst it may be organic and smells wonderful, is highly flammable and has a very low flash point (not good). Once you're happy that the environment that you're going to be using it in is relatively safe (no blow torches or soldering irons in your printing space, and you're a non-smoker) then it's not as noxious to work with compared to other solvents if you're careful, but you do need to take care use precautions to avoid skin contact and keep your hacker space well ventilated. It's actually useful as a cleaning and degreasing product on it's own and does have some other uses aside from just dissolving HIPS, and it's not too hard to get hold of.

The other issue is of the types of filament that it will dissolve. Some will tell you that it won't dissolve ABS but will dissolve PLA, others will tell you that it's the other way around. The truth is that there is so much filament around isn't always strictly what it says it is on the tin. So, make sure you test your filaments in Limonene first - just get a jar and drop some filament in there and leave it for 48 hours - you should get a pretty good idea as to what resists it and which ones will dissolve. I've had both ABS and PLA filaments dissolve in Limonene, but not all ABS and not all PLA. I've no idea how amphora (Colorfabb XT filaments) behaves with Limonene yet as I've not tried it.

Also, you may find that the rate at which HIPS dissolves isn't particularly quick and that after 48 hours the filament you thought was resistant may even start to soften. For that reason I would recommend an ultrasonic bath (a steel one) which aren't too expensive and will greatly accelerate the process, providing that your prints are sufficiently robust enough to endure it.

A great test is to print a Hilbert Cube in a suitable non-dissolvable filament of your choice, combined with HIPS.

HIPS is not too bad to print with either. It prints a lot like ABS and is much more stable and less messy and with much less stringing than PVA. HIPS is useful for other applications, not just support material, unlike PVA.