Keep blowing a fuse

Whats up fellow f-bod drivers.

I was wondering if there is anyone one who can help me to determine whats causing my tail lamps fuse to blow. I recently upgraded from a 95 Conv. V6 Camaro to a 2001 SS Conv. M6. I was driving home a couple of days ago while it was raining and all of a sudden my gauge cluster lights, radio lights, and steering wheel cntrl. lights went out. It was already late and I assumed it was a fuse and I would just replace it the next day. Right away I checked the dimmer fuse, but turns out it was my tail lamps fuse (20amp). I replaced it and went to the store later and it went out again. After a whole box of 20 amp fuses I tried a 25amp just to see how long it would last but I didn't get very far . So now I'm stuck trying to figure out whats going on. It's not the first time it rains, it was raining when I bought it and nothing happened. Any suggestions?
I haven't done anything to the car (bone stock).

Any help would be appreciated,
Thanks.

Does it blow as soon as you put it in, or does it take a little while? If it's instant, wire shorted to the chassis somewhere? Is there water in your tail lamp case? Is everything in your lighting system stock or aftermarket? Do you have the right amp. bulbs in there? If you can pull out the taillamp out, wait for the fuse to blow and feel if the wires to your lamp are really hot. Just some ideas I'm throwing out there.