best way is to get a mate to go around the car with a hose while you sit inside looking for leaks. Another good way is an automatic car wash as sometimes you need high volumes of water to replicate rain.
If the door seals are stuffed, they'll be all hard, cracked torn, chunks missing etc. If they are in reasonable condition, it might be a matter of adjusting the door catch to pull the door in tighter against the seals (if water is leaking though the seal). Sometimes if it's only the top door frame portion of the seal leaking, the only fix is to bend the upper door/window frame in. Wind the window all the way down, knee on the inside of the door solid metal part not the door trim... grab hold of the top of the door frame and pull towards the car a few times. Sounds rough, but it's the only way to do it (we used to do this at Holden dealers to fix water leaks and wind noises, particularly on VN-VS)
I'd also be lifting up the carpet and drying it all out. If it smells mouldy, you probably need to pull the entire carpet and underlay out, hang it on the clothesline, hose it off and let it dry out & spray some deodoriser on it before refitting. If you let the wet carpet sit in the car, it's going to stink and rust the floor out