Alpine R-Type components

no no no, , its just the woofer, no tweets or anything else under the seat, JUST THE WOOFER!

Using a woofer from a component set as a bass fill speaker is a common techniqe especially in the SQ world.  I use two 7" ScanSpeak woofers designed for a component set in .45 CUFT sealed enclosures in the front of my car for front bass fill.  And like Alpine Guy said, if you design it correctly, a sealed enclosure will dramaticly increase a woofer's power handling capability.  My drivers are rated for 100 watts and are driven by 250 crossed between 60Hz and 200 Hz.  Have been for 3 years now.  Component set woofers are rated for free-air (infinite baffle) installation.  This is the worst case situation for a woofer.  The same driver in a sealed enclosure could handle 3 to 5 times the rated power, especially when using a proper band-pass filter crossover.

With reference to DYohn's statement about the infinite baffle scenario, I have installed the comp speakers as described in the topic start, and whilst they are a big improvement over the OE ones, I thought they would carry more bass, since they are based on a subwoofer design. Is this because of the door enclosure they are in, does it require a smaller enclosure to emphasize the bass? If I simply turn the bass up, it just vibrates the door internals.

I am reluctant to mess with the HPF LPF settings, following Alpine guys comment;