Seriously? I like shooting in the rain, less people around usually. There's some skill to be learned in it, atmosphere is obviously different. Rain doesn't act on the bullet as much as you'd think due to velocity, but it does happen. Chances are you won't be shooting in a goddamn downpour anyway. As for comfort, we usually would setup one of those portable awnings or whatever you call 'em. You could make one with PVC pipe, a tarp and some bungee straps. A little dry spot on the firing line just for you and your buddies.
But training at Ft. Lewis where it rained all the time, half the time shooting in the rain was no different than shooting in the sun. Nothing changed really, you just sucked it up. But I'd personally prefer either the gortex suit or the goretex wet weather gear as a minimum if I didn't have an awning to stand under.
Worst part about shooting and living in the rain is keeping the damn weapon clean and rust free.