I plotted these distances on my Nobletec. Boat Launch to the Mouth of Work Channel approx 26.5 NM, then accross to Goose Bay another 15.5 NM, using direct lines. Minimum of 42 Nautical Miles or just shy of 78 KM's. All in all quite the long haul.
Kris the last time I fished Work Channel was 1995, and I understand the road has been improved, but at the time it took 2.5 hours to travel the 12 KM's from the highway in. One time I lost nut on my hitch ball, another time I saw the molten remains of somebodies nice aluminium boat and a scortched hillside(battery arched and ignited gas fumes of too many jerry cans), third time we got a flat from the broken peice of somebodies kicker skeg. Not to scare you, but you have to be self-sufficient and prepared for anything.
First and foremost you need a 4WD to even think about launching on the beach. No ramp, just round beach rocks that will try to swallow your vehicle and trailer. There was no docks or anything when I went there.
Second no gas/no ice. My guess is that with any boat small enough to trailer in but big enough to fish safely your looking at 20-25 litres an hour of consumption or more. Round trip to the head you would be burning a minimum of 50 litres. Bring lots of jerry cans and remember my story of the molten hull and scortched earth.
This is wilderness camping and fishing period. No amenities. We never ventured further than the mouth and you would need a good boat to get back and forth to Dundas safely.
It would be roughly the same distance out of Prince Rupert Harbour where they do sell fuel, although your run is more in the open. If you are looking for an alternative to Kitimat, there are areas to fish out of Rupert that are a lot closer.
When I lived there, Work Channel was a 2-3 day drip done usually by locals as they were close to all the amenities. Most people just fished the mouth. If your boat is big enough to go to Dundas, then you did it out of Prince Rupert.
Good Luck