By "mobile office" are you talking about something with wheels on it?
In the US a trailer or motorized office like that would usually be titled as a "recreational vehicle" to avoid stricter requirements a "home". (US Department of Housing and Urban Development rules).
In the NEC that puts you in Article 551.
551.45 Distribution Panelboard.
(A) Listed and Appropriately Rated. A listed and appropriately rated distribution panelboard or other equipment specifically listed for this purpose shall be used. The grounded conductor termination bar shall be insulated from the enclosure as provided in 551.54(C). An equipment grounding terminal bar shall be attached inside the enclosure of the panelboard.
(B) Location. The distribution panelboard shall be installed in a readily accessible location with the RV in the setup mode. Working clearance for the panelboard with the RV in the setup mode shall be not less than 600 mm (24 in.) wide and 750 mm (30 in.) deep.
Section 551.45(B) was revised for the 2008 Code. Some recreational vehicles have expandable room sections (or slide-out rooms) that are in a stowed position when the vehicle travels from place to place. Working clearance in front of equipment in an expandable section must be maintained when the section is expanded in the setup mode.
Exception No. 1: Where the panelboard cover is exposed to the inside aisle space, one of the working clearance dimensions shall be permitted to be reduced to a minimum of 550 mm (22 in.). A panelboard is considered exposed where the panelboard cover is within 50 mm (2 in.) of the aisle’s finished surface.
Exception No. 2: Compartment doors used for access to a generator shall be permitted to be equipped with a locking system.
(C) Dead-Front Type. The distribution panelboard shall be of the dead-front type and shall consist of one or more circuit breakers or Type S fuseholders. A main disconnecting means shall be provided where fuses are used or where more than two circuit breakers are employed. A main overcurrent protective device not exceeding the power-supply assembly rating shall be provided where more than two branch circuits are employed.