Betagirl... you are not being a wuss for not wanting to ride 300K in the rain.
You did it once... you don't need to do it again.
Doing a 300K should be a little bit fun... and it won't be in the rain.
Look, you do this for fun... not money from a sponsor... so don't worry about passing.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"