Only useable space I have found in the dash is on the side of the steering wheel.
I was thinking on monting "everything" on that panel so that it all comes out together. "Everything" is TPMS, OBDII adapter, wireless USB hub, radio (HQCT or the venice 7) and 5V converter.
But there is not a lot of room....
btw. There is two chairs in the front of my car :-) I have a fireextingisher at the driver seat and first aid on right. But maybe you have fireextingusishers too?