I don't think that snowload should be a problem. I have had my 1990 Airex since June last year, and I have been on top of it two or three times sweeping off cedar needles. I weigh 200 plus pounds and walk around up there just fine. There is little or no deflection of the roof. That means that the point load is pretty high where I step.
If you think there is too much total weight on the vehicle I suspect that you could just sweep it off as it accumulates. If you do, be careful cause a plastic cover is really slippery when it's covered with snow.
You must live in a harsh climate? Smile.