Our diesel truck has about a 250 mile range when we're towing the fifth wheel. We try to stay on the top half of the tank so that means we're filling up around 150 miles. No problems finding diesel.
Even so, we carry extra diesel with us because we can't predict when a service station is going to be out of fuel for a few days, until the delivery truck shows up. Apparently they can't predict it either or they'd have deliveries more often!
The only place it is a concern is on the Dempster Highway where this the distance from the start of the highway to Eagle Plains is 370km (230 miles).