80 ft/lbs should be Ok for steel wheels like that. Check the torque again after about 5-10 miles. If they are still tight then you should be good to go. Most alloy wheels should be torqued to 100 ft/lbs. Not exactly sure why. Maybe more expansion and contraction than steel would cause the nuts to loosen. On any trailer it is always a good idea to check the torque several times a season. Tight turns with a double or triple axle trailer will really put some stress on the wheels.