All these nice sayings come to mind...
1) If a tree falls in the woods and there is nobody there to hear it, did it make a noise? Or... If a cat is in a trailer and nobody sees it, is it really there?
2) Forgiveness is easier to get than permission...
3) Don't ask... don't tell!
4) don't worry, be happy
Honestly, I think the rule is probably intended for dogs who need an 'outdoor' litter box. What will they do if they find out? Shoot you?
Here's your cover story: "Oh, I thought that meant 'no pets on the grounds'... because after all, inside my trailer is MY PERSONAL PROPERTY, not yours " (or something like that).
Hey, its the only way to be sure!