Its best to chain the rear, or front+rear, never just the front. The tendency to oversteer is dangerous. This is part of the reason some folks prefer FWD for snow conditions, they don't know how to regulate throttle to control oversteer (in RWD), and end up out of control. Typically in snow its best to have the drive axle be the heaviest one. As most cars are front heavy, FWD results in better traction.
In my 2WD light pickup days, I would put 200-400lbs of sand/salt in the bed. Combined with good snow tires, I could typically out drive most vehicles with summer tires (4wd included). One winter I had summer tires on the front, it was an interesting year, the tendency to understeer was hard to control with the heavy front brake bias, but the E-brake did an okay job with enough forward planning.
Lockers are important once you start lifting a drive wheel. For rear heavy vans this may not happen, as the front lifts first in most conditions. For these vans a limited slip (Automatic torque biasing or clutch type) may be a better choice. Though for the budget oriented the luncbox style locker may be a good option.
