99 Hyundai Accent 1.5 liter

I have a 99 hyundai accent that is eating up plugs and wires weekly! Not sure why. Also, was told this is why my exhaust manifold had a huge crack all the way around it and my cat converter is cracked. My husband said the cat conv was red hot. The car doesn't run on all cylinders if it gets wet either. Replaced the coil, plugs and wires and a few hours later they were arching again. Any ideas as to what the problem could be? Don't want to put a bunch of $ into it if it isn't worth it!