The Revelator (Story Mission)
Just before your Resistance Points in the Holland Valley peak, you'll get word of a tank-truck leviathan terrorizing the roads. The Widowmaker truck from the mission of same name can be handy here.
Journey to the first marker, and find only carnage in the Revelator's wake.
Revive the resistors, then pile into the turret truck to make a stand at the next roadblock. Even with extra companions, the truck is big enough for everyone.
The Revelator will come in from the east. It can take an extraordinary amount of damage, so litter the ground with proximity mines, and open up with the rocket launcher as soon as it crests the hill.
If it still gets past you, hop in the Widowmaker and finish the job. As ever, the Auto Repair perk can be handy here, particularly if the Revelator's rear turret is still intact.
Even when the Revelator is down, the mission completion may not pop right away. Finish liberating the valley for the mission status to update correctly.