Wont start after a hard rain

For some reason, if it rains at all it takes the van a few times to crank up. But if it really rains hard at all it wont crank at all. I burnt up a starter trying to get it started. Oh it will start eventually if I keep trying, probably 20-30 or more some times cranking it. I know its getting gas, cause you can smell it after a few attempts. Most days I just let it sit till the sun comes out for a few days.
I know it needs an O2 censor and a Cat. Converter, but if it doesn't rain it starts fine. If it starts raining after I'm already out running it does just fine.
Any suggestions?