For you not really, but solid box construction if you want. For the sake of car and boot space it would more like solid shelf fixed to car for full bracing with two boxes secured to it for smaller speakers (smaller than you have might be better) to perhaps face forward into the cabin, the boxes could be like the old angled slopped faced pod speakers housings, but not plastic if going 40w or 50w per channel, perhaps made by you or other.

For me these are exaggerations.

and this one

For me those are gross exaggerations and probably not sufficient for number of speaker and location. Size does not always relate to quality too, or the number of speakers or driver cones, often less can be more.

The car and its cabin restrict sound quality but it depends on how much you are bothered about sound quality and how much sound quality you can or do hear. For expense and pleasure the lower quality you are happy with the better but this can be overtaken by ego, envy and competitiveness and any particularly person's taste.

For me the speakers you have are too big and your taste of interior features and fitments is different to mine but these are not a bad thing, as always each to their own.