For a short period of time, the VW beetle had a rain tray on the back deck after louvers were added. The tray did an excellent job of keeping the engine clean and rust free. My '70 Beetle has the metal tray which empties water thru two side tubes.
When they came out with the dual port engine, they increased the number of louvers, but did away with the rain tray which caused a mess of the engine compartment. Some say the elimination was due to the need for increased air circulation, but those who have fashioned a rain tray for their dual port Beetles never saw significantly increased engine temperatures. They probably eliminated the steel tray to save $$ during production.
You could probably fashion a tray without too much trouble, although I wouldn't hang it tightly against the hood so as to restrict air flow.
