Old Mobile Home Electrical Repair
What type of cord are you using? I have never seen a type of cord that it is rated for direct burial.

Article 550.10 is pretty clear regarding mobile home power cords but it is at the beginning of the Code that states you need to follow all listing, labeling, and manufacturer's instructions.


  110.3(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.


According to the Code, you only need conduit where the cord is exposed to damage, passes through walls or floors, (or where buried because it is not listed / labeled for direct burial).


  550.10(G) Protected. Where the cord passes through walls or floors, it shall be protected by means of conduits and bushings or equivalent.


I would just pass the cord through the skirt and not worry about burying it, or install some PVC from directly under the panel inside to the power pedestal and pull the cord into that. You could use a bushing to pass up into the mobile home. It should already have the bushing if it was wired right from the factory. 

Good luck in the spring!