For the small space you have your better off going with a single 15" than an 18. Have a box built right and it'll get just as loud as you think you'll be with an 18. And dump that stupid capacitor you said you have, upgrade your electrical system before you spend more money on your system. The Big 3 is the place to start, buy some Knukonceptz 1/0 wire for cheap and do it right. DC Audio, Sundown, Incriminator Audio, whatever you can find thats within your price range, they're all good brands. And have someone that actually knows what they're doing set the gains on your amp with an O-Scope, chances are thats why you blew your old subs.