There are other brands like Pelican at 1/3 of the price. If you're only concerned with keeping the gear away from the atmosphere when down here, and there's no problem at home, then you do pretty well with the cheap resealable plastic boxes you find in supermarkets for keeping food in in the fridge. If you look around you'll find some pretty big ones.
I do use dessicant cartridges here, but they go off incredibly quickly. A freshly charged one in the open inside my house is saturated within about half an hour. Something that works well is to wrap each item in soft cotton cloth, as that also absorbs a lot of moisture. I ordered a Pelican case look-alike, but in the meantime I found that if I zipped up my camera bag (a fabric backpack) immediately after accessing it, and put it both on and under freshly laundered tee shirts, then moisture doesn't seem to be a problem.
I wouldn't use just plastic bags/boxes as you can get condensation inside the plastic. Fabric is much better.
What Jesse says is most important here. A/C will destroy your gear - never keep it in an A/C environment, or if you do then warm it up very slowly (many hours) wrapped in cotton fabric that can breathe - ie. not in a plastic bag.
Another important thing that you've undoubtedly not considered. Your camera sensor will get dirty and you need a means of cleaning it. AFAIK there is only one company that makes the products that you will need. I strongly advise you to go to their website http://www.photosol.com/swabproduct.htm
immediately, look up the products your camera needs and buy sufficient for at least ten sensor cleans. Also get the material you need to clean lenses, and get a Rocket Brush. You'll find yourself using this very early on down here!
When are you coming down? Scubaldy needs the equivalent for her Nikon D70 and she'd greatly appreciate it if you could order for her at the same time, and obviously bring it with you. She needs Sensor Swabs size 2 and fluid E2 for the sensor, plus Rocket Brush and lens cleaning materials, and I've just checked that you need exactly the same for your 450D.