Ok, from my experience a tonneau is a great protection from clueless people and a fair protection against weather, although the top (and side windows) are better at the latter. The only times my car was left outside in the rain overnight were Carlisle or the Tour de Smo', and I always put the top up overnight if there was a chance of rain. My tonneau sagged, pooled, and would eventually leak if there was much rain, but the top did not. The only rain intrusion there was around the side windows.