I've put literally several hundred thousand miles on my rear wheel drive vans. Had a '98 Chevy 3500 Express EB I drove the snot out of all over America, and now have had an '08 GMC 2500/3500 Savana EB for several years. I've never worried about winter, from up around the northern reaches of the St Lawrence Seaway in Quebec to 'Snowmaggedon' in DC and VA years ago, to one of the worst winter storms Oklahoma has ever seen, where literally 30-40 power poles in a row had been knocked down from ice load, time and time again in various small towns. Fargo ND, and Maine, etc. Had more problems getting the 6.6 diesel started in Fargo at 25 below zero than I ever had getting the van anywhere over snowy or icy roads.
I'm always loaded, too, well most always. When up around the St Lawrence, I came home empty, but don't recall any hard times coming down through Canada and Maine in Feb. I don't recall ever getting stuck, actually, in my Chev or GM vans for any longer than it might have taken to rock it 2-3 times. I've run Michelin LTX M/S2 245/75R16, summer and winter, with terrific results. The current set still has more than acceptable tread after more than five years, but I'm retiring them soon more from age than anything else. They've been on since Oct 2012 and have seen over 95,000 miles.
Good as they've been in winter, though, I'm getting a 4x4 conversion done once I set it up with Sportsman4x4 in Kamloops who does the Clydesdale conversions. This is so I can go further off-road into remote camping and building sites, primarily in the SW desert. A lot of the other 4x4 conversion companies either won't touch GM vans or won't do a van as old as mine with as many miles. It's an '08, 375,000 miles, and Quigley said no. I understand and respect that. I've talked to a bunch of others and they've said no, as well. One or two just plain never got back to me.
I like what Sportsman is doing with their Clydesdale conversions in Kamloops and yeah, they've been doing a slew of them for BC road crews and such with great success. They do back to 2004 GM vans. I'm happy to keep the IFS, as I have no plans for extreme rock-climbing or highly technical trail competition. I just want even greater assurance when way off-road, winter or summer.
Hope you find a great van that suits you purposes, but I wouldn't worry about not being able to get a GM van converted down the road, long as it a 2004 or newer.
Looking forward to seeing how it goes for you.
OH! Forgot to mention: I bought chains for all four tires but have never had to pull them out to use. Haven't done extreme mountain "chains mandatory!" passes in winter, but have handled everything else just fine. I like the longer wheelbase of the GM EB vans, too, over the wagging tail of the Fords on extended bodies. Easier to distribute the weight of a load or get weight just inside the rear doors without worrying it will lift the front at all.