I currently have a cheap, old 10" bandpass sub in the trunk of my '68, powered by a 200w amp. It actually doesn't sound too bad, but I know there's a lot of room for improvement.

I'd like to upgrade the sub (and amp) and was wondering if you guys have recommendations. I DON'T want to cut or chop the trunk area or rear deck plate. I also DON'T want to build a sub from scratch. I am just looking for a good pre-built sub that will fit into the existing stock trunk, and perhaps some thoughts on a solid amp to power it.

I was thinking maybe a dual 10" or 12" bandpass setup??????????????

thanks for all opinions

Check out the Rockford Fosgate PL1-112, its $209 from crutchfield new or $178 scratch and dent from crutchfield. This is a great sub and will sound very very good without sacrifying all your trunk space like a dual bandpass box will. You WILL be heard coming down the street if you are into that sort of thing.
If you froogle it you'll find it for $169 (search for PL1-112)
Next step up is the Rockford Fosgate PL2-112 for $269 / $229

Be sure to check the dimensions on these boxes to make sure you can slide it into the trunk.