Shouldn't be a problem with smart equipment choices. You just have less margin for error. We tour on a tandem with four panniers and an on-the-road weight (us+bike+gear) around 400 lbs using 35c tires and 40 spoke wheels. As mentioned by others, a good set of hand built wheels with high spoke count will be your most important variable.

Our tandem frame limited us to 35c tires which forced us to run 110-120 psi to prevent pinch flats. This pressure is somewhat above the tire's (Schwalbe Supreme) listed max pressure. You have the luxury of 45c tires so I suspect they will safely carry your touring weight without going much (if any) above their recommended pressure.