There are kickpanels out there for just such a project. The ones I got use 4x6 speakers. I think there is another version out there that take round ones, but not sure what size. Here is what mine look like now that I painted them and the grilles.
I have something very similar that I got from the Paddock. They were offered with Chinese so-so 100 watt speakers or Pioneer 130 watt units. They are made of PVC, so they are not as flexible as the OEM kick panels. They are precisely made as the screw hole in the panel aligned with the hone in the car. Clears the A/C, don't know about a "winter door"