The reason for isobaric is that you need half the air volume to perform the task.
Example 1 x 10" require 2cft, running 2 in a isobaric format I only need 1cft.
Therefore the 10" or 8" depending on what will fit isn't compromised. The bass will also be cleaner running isobaric, with lower hz handling.
The rattling isn't an issue, I'll fix that, I know how to strip the back section in less than 10 mins. Them to provide sound proofing and refit shouldn't be an issue.
What I don't want is a mass of space used in my car which I would otherwise use. I like your setup
Dave but I use my boot and don't really want to have to compromise with having to lift the sub in and out based on my boot contents.
Budget just on the sub section including amp will be about £600-800. As mentioned I'd really like to try the Boston Subs, they've been around for a long time and never ward a bad word.
At the end of the day I want a quality sound, which is why I want to go isobaric, having a more controlled bass.