Remember all those times I've said you need to know more than just the NEC? Well, this is one of those times ...
First off, your work is likely to be inspected / approved by an additional authority - a 'mobile home' bureaucracy of some sort. They may even require you to get an additional license if you do anything more than simply run the service; the final hook-up is considered work 'on' the trailer.
The panel in the trailer will have a sticker inside that says something like "To be supplied by a service no greater than 150 amp." Well ... big surprise here ... the HUD weenies understand that to mean that you MUST provide a 150-amp service.
You, as the electrician, are expected to run your service to a point under the trailer, then provide a place for the trailer guy to connect the tail from the panel. The HUD specs want you to run your pipe at least 24" underground ... a bit more than NEC requirements.
Since the whip is of a finite length, you need to be sure you go far enough under the trailer. Hope you like digging while laying on your belly. Don't forget to tuck-tape the moisture barrier when you close the trench.
