How to deal with paranoia about fuel leaks

Well, don't take too much away from the VW fires; they caught on fire a LOT. So that alone will give you a false perspective on how often gas fires take place. If the float sticks, even with the drip tray you could have a fire. And not all gas on hot manifolds catches fire either, so that is in your favor. The manifolds hanging out there in the air means it won't pool up any where. Slant 6's just don't have any sort of reputation for fire problems.

Fix the leak and be happy; I don't think the tray is going to do you any good whatsoever in case of a float sticking/breaking.

BTW, that carb and intake getting heat from the exhaust manifold is good for your mileage; helps keep the fuel from condensing out of the intake air.