With the kick panel vent off just stuff the shop vac hose in there to suck up the leaves. On the passenger side open the recirc door and try to do the same thing on that side and in front of the heater core. You'd really have to have a pile of mulch in there for it to hold enough water to leak in to the cab. The wiper linkage area under the cowl really doesn't hold much - it all washes down in to the vent areas.

The side vent windows leak on just about every one of these trucks. Runs down the door and puddles just below the dimmer switch. They do repop glass seals but often doesn't help with the leak. A drip coming down the fire wall is often a rust hole in the cowl under the wiper linkage. It's less than easy but ya need to get your head under the dash in a heavy rain and find the highest wet spot then poke around under the hood / cowl on the other side. A garden hose will also work.

It's a Dodge, it leaks. It might just be easier to put a drain hole in the floor. When I did my cab floors I used aluminum diamond plate instead of sheet metal.