Section 511.9 refers back to Section 501.15 with special reference to 501.15(B)(2). This is good because there are a several exceptions to 501.15(B)(2). The one you are interested in is Exception No. 1. If more than 12? of the RMC stub-up is underground and it runs 12? past the upper boundary ? you don?t need any seals at all. Otherwise, you need an aboveground seal within 10? of grade (the lower boundary).
A minor caution: review Section 511.7 for some additional requirements for wiring and equipment above the Division 2 location. It probably won?t affect anything you plan to do already but it?s a good idea to check.