So, my question would be, what are you planning on doing with the dog if you want to go with the family on an all day outing and can't take the dog?
You are getting a working breed so it needs to have a job. A tired dog is a good dog. And a BMD will need ALOT of exercise. 
There is not an rv park around that will not frown on leaving an animal, especially that size, unattended all day in a trailer. Not to mention the other campers if he barks all day.
Forgive my " political incorrectness" but Just saying. Doesn't seem fair to the dog to me.