1974 Chevy Impala will not start when wet?

I have installed the Ignitor last year. 1974 Chev 350 in my 1941 Ford Sedan Delivery street rod.
All was/is OK but not sure. I travled a lot with it in and it has great response and starts good altho I do think the gas mileage has dropped!
I have had this other problem 4 times now. Twice last weekend at a car show in MI. 4 days and I do not think it stopped raining at all.
Well when it rains while the rod is sitting and it gets wet under the hood, louvered hood, when I go to start the engine it acts like it is totally off time and will not turn over completly, it like locks up and makes a Loud noise while the starter engages and tries to rotate the engine.
I can bump the starter a little at a time and after a while it does start to turn over more and eventually starts.
After that start all is well. I can turn it off and start it right up, no problem.
I bought a tarp at a hardware store and the rest of the weekend I covered the engine and no further problems.
I also have another intermitent problem, engine stops running like it is out of gas. 4 times when I was below 1/4 tank and I found out I could restart it and go on. So I blamed it on a bad fuel pick up in the gas tank. On the way home from MI. It stopped while leaving the toll booth with 3/4 tank of gas. I was able to limp to the side of the road. Again I was able to re start it and travel the 70 miles home. I just remembered though that did happen on 2 road trips and killed on the express was at highway speeds. I coasted to the side of the road and gather my senses and then tried to start it and it started right up and I was on my way.
I know lots of problems here but I just want to mention them as they ar all intermitent and who knows if they are related. I do not think. Well I do not know for sure what to think.
Can you help?
Sincerely,
Don in WI. NSRA