Hi Pete. I guess it depends on what size vents you are using, and how much panel space you have available. I used the large vents and placed them on a sub panel that mounts to a bracket riveted to the fuselage side skin, and also to the bottom flange on the instrument panel. I don't have any good photo's in my log, but will get some this afternoon. I made this panel large enough to enable the install of the vents, two jacks and one push-pull cable on each side (left side for park brake, right side for firewall heater valve). The panels were triangular so that there is no interference with your knees. I placed the jacks here as there will be a pocket underneath to take any ANR battery packs etc.
The downside about this approach is the you will need a few more rivets down the side of the fuselage where the standard bracket goes, and you will need to make sure any bracket matches the fuselage curvature well.
Tom.