Do they still need packing to get the best out of subs?

Some fibre installs/boxes don't seem big enough to pack hardly.

Just wondering if i'd need to build something a decent size in order to pack, or if i could get away with taking up little space in the boot.

Each sub has its own recommended size (CUFT) for the box its to be mounted in, only as a guide but they do sound better if you can get close to this size. If you can fit packing in then do it as in fibreglass installs it does help with sound, but dont worry about it to much if you want to save space.

ok. How much does it affect the quality of the sound?

Looks quite small, but still nice.

and surely this can't be big enough for best qaulity...