Good question. I have deinstalled a couple of the furnaces and the plate that the chrome cover sits over is made as an assembly. They are 4-6 inches in length. The intake and exaust tubes insert into the corresponding tubes in the furnace. I have not gotten out a level to check, but I bet if you could you would find that those openings are tipped down so water will run out by gravity. This would be caused by where the vent is cut in the skin, or by mounting the furnace up a bit in relation to the holes. If you think about it it is a simply elegant way to keep from obstucting the intake/exaust. When the unit is running I bet there is enough heat to keep it all dry!
BTW Suburban says that if you add ANY type of cover or screen to their furnace exaust, even to keep out the wasps and mud daubers you will void your warranty. So be sure to take it off before you take the unit in for service!
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato