Underseat

The midbass if they aren't in the door need a box with the necessary volume.
So there must be the necessary space under the seat.
In this configuration the low frequencies should benefit, because they are loaded with the footwells under the dashboard.
The mid frequencies play with the reflections, it is difficult to say how they will be reproduced, but in this regard for me the suggestion of Andersonix is also valid.
In my opinion it would be useful to try the mids also in the dashboard.

If the midwoofer goes in the door i think that the work for the assembly is greater than a simple box under the seat, and perhaps also less effective for the low frequencies.
So at this point, you could try with the less demanding work.
However we don't know which speaker system will be used and with which filtering.