I decided to not bother calling SMB West and implemented my own solution; a variation on the side screws that a few folks found on their brake lights.
The side screws provide security that the whole light won't come too loose but they are often installed without the needed tension to pull the brake light outer flange tight against the penthouse.
I thought combining the side screws with small right angle brackets would work better. However I didn't like the size of the screw holes on the smallest right-angle brackets. They were too big as they were designed for seating flat head screws and sheet metal screw were more appropriate for providing a secure grip in the plastic housing. I also wanted a bracket that was easier to bend for reasons you will see later. looking thru the various bins of hardware in my garage I found the perfect candidate; a 1/2" pipe strap.
A couple of cuts with tin snips and some straightening in the vice and I had my two brackets.
Note I purposely bent the brackets to be less than 90* to start with. Now I had to drill holes in the sides of the brake light. I didn't want the side screws to run into the post for the lens screws so I wanted to make sure they entered into the bottom half of the housing, which I marked with a line on some masking tape.
I then held the each bracket in place as "sherryfromsf" held the light tight against the penthouse and I marked where on the line I would drill the hole
I then carefully stepped up thru drill bit sizes until I found one that would allow a tight fit for the sheet metal screw and not crack the housing.
After drilling the holes I rebent the brackets to now be much greater than 90*.
This new bend provided pressure to pull the housing against the penthouse as I tightened the screw.
Not a thing of beauty, but certainly provides the needed function that the SMB implementation didn't. And it cost me $0.00 it was sourced from bits in the garage.