Be sure to remove the plastic liners on the fender wells when climbing in. This will show leaks coming from the side moulding trim, antenna mast and fuel filler neck.

I forgot to say, check all drains. The spare tire well has its drain hole, as do the fender wells right behind each rear wheel. All 3 should be clear of debris. Poke a screwdriver from the underside to clear the drains out.

Also, the bumper corners have mounting brackets to the fender (Euro versions) or the rubber ends have mounts going into the fender (Euro and US). Since the US have the large rubber covers, I wouldn't worry about them that much, but just the same, inspect for any signs of leakage. The US bumpers use two out of three holes for mounting the cover. The third (middle) hole has a rubber plug. Euro models use only the middle hole. Leaks here can get into the fender well. Coupled with clogged drains, they will pool water.