PCAR-YVR, where have you gone to for advice in town?
The 8 inch in the door is a good idea but that install is horrible. Not sure if you have seen this post on renntech before but this is the best 8" install in the doors that I have seen to date. Those Kickers are greta subs at a great pricepoint too.
http://www.renntech.org/forums/index.php?showtopic=14162
My idea of having the subs behind the seats should work out really well. There have been a few posts about this and I have collected some pictures over 2 years of installs that I have seen. However, no one has gone to the extent of actually removing the firewall carpeting and insulation and doing a custom fiberglass enclosure as of yet (that i have seen). Hopefully I will be able to tackle this in about 2 weeks time. I will create the fiberglas enclosure and then wrap it in real leather to finish off the look. If this works out well I may be able to make a mould for other members. I just need to know if people would prefer a 2 piece design or a 1 piece design. These are the subs that I am thinking of using as well. Cheaper than the Pioneer, the new JL shallows coming out, excellent quality, very little space needed and a super low price point as well.
http://www.edesignaudio.com/product_info.php?cPath=1_21&products_id=106