Well, the Fli's are certinaly going to be better than the OEM equipment, but they arent fantastic.

But, for

£39.99

(according to Halfords, not checked anywhere else, was first on Google) they shouldnt be too bad.

Most head units arent going to put out much more than 15WRMS, so to really get the most out of them an amp would be best.

They would certainly perform better in the doors than behind the seats!

Subs work fine behind seats or on one side of a vehicle because generally the Q

(directivity) of a speaker approaches 1 at low frequencies, which means it is omnidirectional, so your ears won't be able to hear where the sound is coming from so much.

As the frequency increases, so does the Q value, so the sound becomes more directional and IMO it would be quite annoying to be able to hear mids from one side of the car only!

If you didnt amp them, they should still perform better than the OEM stuff.

If you did want an actual sub, the smallest

'proper' sub I have ever seen is 6inch, and it was a JL item.

It probably wont fit in the OEM box, but perhaps it would be possible to fabricate something that would allow you to fit it in the OEM location?