One thing to take care about is that suction cups work because of (duh) suction. Basically, the cup is held in place by the pressure differential across the membrane. That pressure differential varies with altitude, so a suction cup that holds a certain load on the ground might not do so at cruise altitude.
Back when we used cameras to validate turnpoints in glider contests (these days we use GPS), I built a mount with three suction cups to secure my turnpoint camera to the canopy. On one task I climbed all the way to the contest ceiling of 17,500 feet, and soon after the camera and mount fell off into my lap. It held fine when I stuck it back on, but it was kind of a wakeup call.
If I recall my altimetry correctly, at 18,000 feet the ambient pressure is half that of sea level, and half of the atmosphere is below you. I think that means that a suction cup at that altitude has half the holding power of one at sea level, but I'd have to think about that.
Thanks, Bob K.