I am still saving for my system, but I have read a number of the stereo posts. Regarding mounting the amp on the steel wall by the gas tank, a number of people mount it on a MDF board in front of the gas tank - you don't want any leaks there! They either suspend a small board from the package shelf with "L" brackets to hold the amp, or fabric cover a large board they place against the steel tank cover.
On your sub, I have been hearing good things about the Infinity BassLink - a 10" servo controlled sub/10"passive rasiator/200watt amp in a 1 cubic foot box.
http://www.infinitysystems.com/caraudio/product.asp?ProdId='BASSLINK' Various reviewers say it sounds better than the Bazookas, maybe someone else has some experience with them. Or Continental Imports has a Blaupunkt powered sup that is small enough to keep in the cabin.
http://www.continentalimports.com/cms_265.html I haven't heard either of these, so you might want to listen to all 3 before buying. Good luck with your install.
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John
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E