With the owner's permission, I've lived in a trailer on his ranch property for over 25 years. Do I now own the land on which the trailer sits? What's the law on squatter's rights?
All depends. You usually only can acquire land by "adverse possession", if you are there in the open and "notorious" (e.g.. so anyone can see it.) You can also try possession under a claim of right (e.g., as if you had reason to believe you had the right to be there and keep the land, perhaps because you were watching the other property for the owner, and he said I want you there and if you look out for the rest of the land, this land will be yours). A tenant under a lease doesn't get to keep the house after paying rent for 25 years, for example since this was by "permission".
But you need to contact an attorney in your state who can explain what your state's rules are and how they apply to your exact situation. It's worth a shot.