Lots of people with homemade class B's say to not locate a ceiling vent over the bed due to inevitable leaks, whether failed sealing or failure to close before a rainstorm.
My ceiling vent is located at the peak of my high top, and I tend to cook on a single burner stove directly beneath it.
For Me, efficient 12vDC computer fans with speed control is the way to go. My original 4 inch Nicro marine style mushroom vent could not move enough air on its own, but I can force feed that aperture with powerful enough computer fans to exhange all the volume of air inside once every few minutes if necessary, and I have several ideal for improving airflow using even less electricity, but these are not really required.
Also a fan should be shrouded if placed in a window or vent, otherwise a significant portion of air moved, will be recycled air, whereas a fan with a shroud displaces all the air around it. The key is to exchange inside air for outside air, not just have an interior breeze to cool the skin, but both is better. Exchange inside air for outside air, and blow that cooler outside air across one's skin.
I use powerful Vantec tornado fans 80 and 92MM on a voltage speed controller for interior air circulation, and for white noise when those dang kids have their meltdowns, or the dogs start barking.