We live on a boat and are paying slip fee, how do we enter the deduction in turbo tax?

The slip fee would not be deductible.  The slip fees and other expenses connected with the boat are nondeductible personal expenses.

If the boat had a loan, and the loan was properly secured, it might be classified as a "mortgage" and you could deduct the interest.  You can deduct property taxes you pay on real property (land) that you own, but that does not apply to the slip fee, even if the marina owner uses part of your slip fee to pay their property taxes.  Other household expenses are non-deductible personal living expenses, even if you are living on a boat.