Having your plate under the camper overhang could be a violation if stopped, the law states the plate should be in 'plain view' of any LE officer at any time. Being the law abiding person I am, I affixed a license plate bracket to my camper and I take the plate from the truck step bumper and put it on the camper, in plain view.
I don't have a front plate either, Michigan don't require one and far as plate readers on toll roads, I have an Easy Pass which covers most toll roads.
Prior to the easy pass I did 'run' the Illinois tool road one time and never got a bill so I guess overhead readers aren't all that accurate.