Do you need to contain your passport etc. in a ziplock bag if you wear a money belt (to protect against moisture)?
I found it a good idea and worthwhile. Some do come with a plastic insert to protect against moisture
they make them that way that moisture does not get in I thought the brand Eagle Creek that I've had since 2002
We everything in a bag in the summer time especially if in a high humidity area. For money we use the snack size bags - perfect for Euro. For the passport use the sandwich size.
I do as Frank mentioned. Better to have the extra layer of protection than to risk getting things wet either though sweating a lot, getting caught in a drenching rain, or falling into a lake or river (it can happen, and all 3 have happened to me while traveling!).
Good idea to have the extra security of a zip lock bag. I bring several sizes along for backup. Light weight and convenient for multple purposes.
A billion years ago, I worked ticket sales at a major theme park. Because of the heat/humidity, the money handed to me was often dripping with sweat.
Take my advice. Use a ziplock bag, just for your own comfort.