Nigel
I may have misunderstood your meaning, "200 feet off the deck" says to me a coudbase of 200 feet with the hills rising into it and gaps where the hills are lower than the cloudbase. I think what you mean is 200 feet clearance above the hilltops which is quite different.
I think Shy Torque summed it up very well in his post above. Just say no in bad weather.