Issue I am testing the rental management add-on for our client, Kreg Therapeutics. I merged the rental objects into their database (fob file is ODTRM1.17 NA4 SP2  Rental Management Release Update.fob).
I created a role called RENTAL-USER and added the permissions as outlined in the Excel spreadsheet (ODTRM1.07 Rental Management Object Numbering and Permissions Base.xls) (see attached Word document, rental permission.doc).
I added a test user and assigned it to the ALL and RENTAL-USER roles. When logging in as this user, I get only the History, Reports, Periodic Activities and Setup groups on the Rental Management menu. . I do not get Rentals or Order Processing.
Do I need to add the Navision table objects to the permissions in RENTAL-USER? If so, should they be read-only? Or, is there some combination of roles that I should assign to the user (e.g. S&R, Q/O/I/C/R)? I suspect this also pertains to the posting and manager permissions.
The user you created with the Table Data and permissions Dianna sent you are correct but there are additional roles to setup.  The Rental Management is based on Sales & Receivables, Inventory and/or Fixed Assets.   Adding roles allowing access to these areas should resolve any permissions issues.
Attached is a spreadsheet with roles permission as an example.  With this setup, the user can see Rental Process forms and create new Rental Orders.  (Which was missing previously)  Also, refer to document - Rental Management 1.07 - Implementation Checklist for more details.  

Developer's Notes:

They must add the Navsion table objects to the permissions in RENTAL-USER. Our Rental Management is based on the Sales Order (Table Sales Header and Table Sales Line). So I think some combination of sales roles can solve their problem. I added the S&R, Q/O/I/C/R role to the rental user. I can see the Rental Process forms. But I couldn't create a new Rental Order. The error is " You don't have permission read Responsibility Center data."  

One role is not enough. At last, I added those roles the rental user:all, "INVT-TRANSFER, POST", "SM-SETUP", "S&R-CUSTOMER", "S&R-Q/O/I/R/C" , "WM-R/PA/A/P/S"  and the role called "RENTAL-USER".  It worked.
See attachment for user roles and permissions setup examples.