engine runs rough when raining or damp

[chevyjr73]

i was just wondering if anyone else has this problem but my truck runs like crap sometimes when its raining outside or very damp. i've had two different carbs on there( q-jet and an edelbrock 1406) and its done the same thing with both carbs. have replaced plugs, wires, cap, even put a new distributor in without the esc module and it still does the same thing. almost seems to me as if water or moisture is getting in the fuel. won't water in the gas cause this problem? it will even backfire and pop a little bit until it gets really warmed up but it only does this when it's damp or raining. i'm wondering if the gas tank sitting sideways between the bed and cab with the whole top of the tank exposed could be letting moisture get into the gas. seems to run better sometimes too when i add water remover to the fuel. any help would be appreciated. thanks.