Interior suction mount for LEDs

Since I have a tonneau cover I'm unable to mount something like a Rigid Dually facing the rear of my truck out of the bed. I thought about mounting something on my rear bumper but for the sake of security I'd rather not have to worry about some lights being easily access able to anyone with stick fingers. Would these brackets (or something like them) be okay to run lights pointing to the rear of my truck from the cab? I'm thinking if I mount them high enough in the back window I should be able to get a similar angle versus having some bed mounted lights.
Does anyone have any insight as to just using a simple mount like in the link below? I would have to line the part of the light that touches the actual window with foam or something to keep vibrations and the chance if breaking the window to a minimum.

http://www.responderpse.com/mbmmaxa-2-suction-cup-l-bracket-for-windshield.htm

 

I think the biggest issue would be the weight of the lights...I don't know if that single suction cup will hold them up.

 

I haven't held a Rigid Dually - are they that heavy? I was thinking worse case I can have a bar fabbed up that connects between the two "oh shit" handles in the back seat. Throw a couple if bends in it and weld some mounting tabs to it.

 

Amazon lists the weight at about 4#'s...I know my whelen warning light weighs about half that...I'd think it'd work, but you might need more than one suction cup.

 

I'll look up whelen as well maybe there's something that will work or give me a new idea. Thanks for your help!