You say the land "sits in front of" your vacation rental property. To me, that indicates that it's across the street from the property and "could" puts it's investment use in question for all I know.
If the land is available for the exclusive use of your short term tenants, and is specified as such in the rental agreement, then you can include the property taxes, HOA fees and mortgage interest on the SCH E. But being across the street (assuming my assumption is correct) the only way I would see it as useful for short term tenants, would be for something like vehicle parking.
Otherwise, the property is personal use and you can only deduct property taxes and mortgage interest (subject to SALT limits) as a SCH A itemized deduction.
