There are a few highly rated HipCamp hosts in our area that have 'U-Pick' farms of produce and/or petting zoo type animals, and they've added a handful of RV sites to go along with it.  

Quote from @James Wise: I've never heard of KS York so I've got no dog in that fight.

Allow a pets and I think you will have a great spot.Would adding that extra space/ spending that money be reflected in an appropriate increase in the property value too?

First of all I put my acceptance criteria clearly in the ad: minimum credit score (enter X amount, 620 is what I use),income 2-3x rent, good rental history, references, no evictions, acceptance dependent upon background check and employment verification, pet policy, desired lease term, etc. so that people will hopefully read that and not come to the open house if they know they won’t qualify.

I may also charge if one of our people can't perform scheduled maintenance because the tenant has not crated an aggressive dog.

Consider all the things that could go wrong and see if the lease addresses them: unauthorized pets or tenants, early termination, security deposit, lease violations, late rent, eviction, lawn maintenance, parking, etc.5.

Each one has a dog for $50 a month.

If it is not behaved such that you would not accept it as a pet, reject it.  

The issue stems from the tenant having to guess/figure out what breed their dog is if the dog is mixed.

No pets?