Yeah, I have some thick rubber flaps over my rear ones now but have been planning to make some out of aluminum or plastic (whatever I end up doing the door panels in) and making it look less obvious. Seems like there's a fair amount of storage space there. I'd want to seal any leaks from the exterior first. I was thinking the space next to the seats would be a good "hidden" compartment space.

I'd also like to see anyone else's approach to this.