I ahve five torque wrenches two Snap on and three Draper, the two Snap on ones which I used at work and were always compaired during use to a calibrated Acratorque tester and never had to be readjusted in 10 years. The others I have used at home for general car mechanics, and on checking them against my Snap on ones are withing a foot pound and also an inch pound.
I do not check my wheel Torques every trip but usally about every two months.
I wonder how many drivers Never check their car wheel bolt torques, so why should Caravanners check the vans bolts. ?