What permanently dark side of the planet? Contrary to beliefs in the '60s, Mercury is not tidelocked. It's rotational period is 59 days, making three complete rotations in two orbits.
You could get around this by having a mobile operating base for any manned mission to Mercury that stays out of direct sunlight to avoid frying its occupants. Its 3:2 spin-orbit resonance means that a single day on Mercury last exactly two Mercury years, or about 176 Earth days - so a single fixed point on the surface would be in daylight continuously for 88 days. Given that its radius is 2,439.7 ± 1.0 km, it has a circumference of 7667.6 km, so you'd only need to be able to move 87.1 km/day, or 3.63km/h.