I once did have to get a plastic shopping bag to put over my Titan engine and it did the job because the air intake draws from the bottom. The exhaust seemed unaffected. I held it down with a little string but this one time I only did because it was absolutely POURING the kind that have soccer moms turn their wipers on high and they STILL can't see you.
In regular rain my engine seems unaffected.
I have rain gear from Wal Marts. Yes. You need those rain pants too.
Lightning not so much.
Here's an older video I made riding in the rain.
YouTube - Riding Cronus in the rain PT 2