I do what DownsD does. Also, use baby wipes. Here is the routine.

Before trip, take shower, apply Vaseline to suspect areas (only need a little).
When use the bathroom, use at least one moist wipe to completely clean all areas of "stuff" and sweat. Reapply Vaseline.
In morning, use one moist wipe to clean all netherly regions and reapply Vaseline.

I did this in the army with sweaty uniforms that weren't washed everyday, and I couldn't shower everyday, and I was in extremely humid environments.
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