fitting 8 inch subs in rear doors?

[Chogg]

I've been weighing up my options and want to see if this is do-able?

One of the many ideas is to get a couple of 8 inch subs and fit them into the rear doors in place of the lower speakers in place (and disconnect the tweeter) That way I could use 1 4 channel amp and amp 2 subs in the doors and do mid / hi in components in the front doors (saves amping 4 door sets and seperate subs in boot taking up more room).

Further to this thread viewtopic.php?f=32&t=10057" onclick="window.open(this.href);return false; I found that on the 5.5 the speakers are on thier own plug after the multiplug for everything except the speaker came off today. I don't know if that means the 5.5 doors don't share an earth with the speaker as that is a very odd way to do it.

Does anyone know how high a rating the multi plug is and would I be able to run a speaker wire rated to approx 300w max through the plug or would I be better running a fresh wire and hope I never need to take the door off?