'Diver. The tires don't cost you more if you switch 'em up in summer; you just have 140,000 km worth of tires instead of just 70,000 km worth of tires
. As a great 'all-season' tire that's not really an all-season, I really liked my Michelin LTX M&S tires. They have great siping, they're quiet, the winter acceleration and braking are very good. Always lean towards the SHTF foul weather performance over quiet, ideal road, high mileage donuts if you just go with one set. I had some of those prior to the Goodyear Silent Armors I have now, and I consider the Goodyears a downgrade; especially as far as braking goes. They were bought during a 4 for 3 sale, so that was a price point decision made before I had experienced them. If Nokian Hakkapellittas LT's come in your size, give them serious consideration too.
All my towing has been a bumper pull cargo trailer, but a 10,000 lb rated unit. Make sure to have lots of weight in your truck, as many others have noted. I always try to keep the bulk of my cargo/ballast forward of the rear axle. The more weight the better, so the less that trailer can try steering you, and you have the requisite traction on the drive wheels.