I picked up my soft top from Vintage Power Wagons about 4 years ago and its held up well in both weather and storage indoors, as far as the canvas itself is concerned. The truck does leak when it rains on it though, but that is through no fault of the top.
As far as weather-tightness any military vehicle is pretty much off the list. The side glasses don't seal to the top frames well at all, and when it rains you will get some measure of water blowing into the cab from various places around the top, doors, and windshield.
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