Had one on a 25ft winnie. Like others have posted only works in low humidity and if it is blowing directly on you. Will not cool down the interior.
What works better is to use a spray bottle of water set to a mist. Use fans and spray your self and pets when you get warm. Stay in front of the fan or if there is a breeze open the windows/go outside in the shade.
We had to dig a trench in 100+ degree heat. Luckily there was a slight breeze. The spray bottle worked well but we still had to stop every 15 minutes and head for shade to cool down to prevent heat stroke.