Go with a 2 part epoxy if your looking for permeant stick

 

Batman. I'm just looking to stick on my old L bracket remote strobes on the new directional bar goin in the back. Assuming I measured right, they should nestle perfect and have the strobe head just below the bar if I reverse the L and stick it on.

 

To give you a better idea of my plan for the warning lights:
Bear in mind, I could get Amber/Green mix if I wanted to, however, I want it to be universal, so if I leave my occupation, I do not necessarily have to get rid of the lights because the green is a dedicated color to my occupation, so they will be all amber.

Two of these. Mounted in the windshield on top, one on either side of the rear view mirror. (Yes, they will fit, but only just.)
LED Quad Bar

And one of these in the back hatch window, which again is a snug fit, but it's better for eyeballing the measurements.
OKTAG Traffic Advisor

And upon further thought, I will wire the two existing remote strobes that I have to be set up in the back quarter windows in the hatch area. And set up the existing dash mount light affixed to my rear view mirror and have this all wired to a manual switch box with a master on/off switch with individual selectors for each of the 4 sets of items. (Windshield units, Dash Unit on Mirror, Pair of Remote Strobes, Traffic Advisor) similar to this one:
Emergency Light Controller.

 

How about double sided foam tape. (3M tape) should hold very well on the flat part of the bar.

 

@Lucky. Good point. Did you see the set up I was looking at?

 

I seen the light stick you want for the back. I installed the same one in the back of my car. it fits well in the back window. I bolted it to the little ledge at the bottom of the rear glass and ran the wires into the gate and into the car next to the factory wiring inside the boot at the top of the gate so there are no wires that can be seen.

 

I'm going to mount mine up top and run it down along the back hatch rail and through the wheel well via the tail light access panel and up that way and put it in a 3 code box with individual item selectors.