I've done that for a while, 400mm prime + TCs + monopod. It's possible, not too tiresome to carry around on the shoulder. It becomes problematic if you want to walk longer distances, e.g. 25km along the shore, and clumsy for BIF.Most professionals using big white lenses in situations requiring moving around quite a bit mount the combination on a monopod. They rest the lens on their shoulder when on the move. The monopod acts as a counterbalance, it also steadies the camera when shooting and is not as cumbersome to set up as a tripod.