Suck or blow... and where's the best spot to do it?

In the bathroom on exhaust. You want to remove the high humidity generated when you take a shower. Excessive moisture is not good inside the trailer. Also, it helps clean the air after utilizing the commode. This is VERY important in a small area, especially when my MIL visits and uses the commode.
A good fan on exhaust in the bathroom can draw air through the entire trailer, too. You should have an exhaust fan above your stove already. As for the bedroom, it can be very noisy when trying to sleep.