The regular Tyvek Homewrap, available in 8 and 10 X 100 foot rolls at most builder supplies sheds water better than standard 1.35 oz. silnylon. the Silnylon will have some mist-through. Tyvek will not. However, it is not suitable for groundsheets on wet ground because it will weep. Compared to anything else, Tyvek is extremely breathable and its bright white reflects a lot of the sun's heat. However, any enclosed tent will heat up in the tropics. A high set-up with lots of flow-though ventilation is a good idea. In that case, any waterproof fabric will do. Therefore, you might as well go with the lightest you can find. I like double coated silnylon which is really waterproof, unlike the regular stuff.

Your clients don't want to hammock, huh? Do they know about all the creepy crawlies down there?