A prime suspect would be the crankshaft position (CKP) sensor which is at the bell housing area. That location would be subject to water and could be failing or have problems in the connector. I'd definitely check the CKP. It's also possible that if the sparkplug wires are worn out there could be electrical leakage shorting out the spark when it's wet or humid under the hood. Check for spark (don't get zapped) and look for water in the sparkplug cable boots at the plugs and at the distributor and inside the distributor cap. The distributor is hard to access, but If the cap is contaminated inside, it'll give you trouble when wet. I don't think the ignition module would be subject to wetness problems unless it's damaged and gets water in it. The coil and module are inside the distributor and may be serviced separately.