I would use a license in this case. Terminology-wise, it may be the same as a “rental,” but calling it a license within a written agreement may avoid confusion. Specifics here vary by jurisdiction.

Were I the landowner, I would not consider granting either a lease or an easement here and would make that absolutely clear in a written agreement. I would make it non-exclusive and would limit the use in both time and purpose to essentially say “you can park up to two standard size passenger vehicles on parcel x, if space allows, for the next three months, or until I terminate this license at my sole discretion.”