The pilot reported that he was taking cargo to a remote mining airstrip when, during the landing roll, the main landing gear wheels encountered several soft spots and he had difficulty maintaining directional control. The nosewheel encountered rough and soft terrain near the edge of the airstrip and collapsed rearward, damaging a fuselage structural bulkhead. The pilot stated that there was no preaccident mechanical problems with the airplane and that it would have been beneficial to have a wider runway and more experience in that type of airplane. Probable Cause: The pilot’s failure to maintain directional control while landing on a rough, soft, and narrow airstrip.