Unless I missed my guess, your using URD for a feeder from the pedestal to the panel in the mobile home. Even if I'm wrong with my guess - URD is a conductor used underground by the utility companies (I think). The NEC in Article 110 Section 110.8 kinda tells me that this type of conductor probably would not be recognized as acceptable for the installation inside the mobile home. Check also Article 550 Section 550.33.
Could not find URD 2224 in the NEC or the UL white book.