You will first have to create in the chart of accounts an income account called interest income, and then create a service item named for int income and link it to that income account.
Then an item for the slip rental. Which account it links to is your decision. Either an income account if the full amount of the slip is paid for, or the slip liability account.
Interest is something you will need to search the web for a utility that will calculate it for you, monthly.
Then each month create an invoice,
line one; slip rental and the amount
line two; int income and the amount
At the end of the year you will most likely have to prepare an IRS form 1099-int for the interest received - QB does not do form 1099-int
