What is the best way to keep an extra set of spark plugs in the interior cabin with out them corroding? Tools rust rapidly because of the heat and humidity.

How about in a sealed container with a silica dry back that is found in dry goods? Or maybe rice?

 

If you don't run trailing ignition you can store them in the trailing plug locations.

 

Looks like you could squeeze the plugs in between the burgers

 

t-g, but when the engine was running like crap, the trailing plugs were just as wet as the leading ones.