As an undergraduate student in biology, I spent several weeks in Costa Rica one summer with an older graduate student on a research project deep in the cloud forest. It was just the two of us, and upon arriving at our site, I discovered that he had arranged a single room for us, one bed.
Mortified but afraid of being labeled prudish or difficult, I made no fuss. I took the lodge owner aside the next day and requested my own bed. The problem ended there, and my graduate student boss never made any physical advances.