The suction cup on my dash cam doesn't hold anymore, and I've only had it since March. I'm tempted to stick it on with some rubber cement or something, but first I'd like to know if anyone has a better solution.
My dash cam (Viofo A119) came with 3M extreme mounting tape, which has been excellent. Might want to see if you can use something like that, since it's not going to be removed / moved once you've mounted it.
Mine's mounted to the windshield, above the rear-view mirror. Right up against the headliner, basically. It's positioned so that I can't even see the dash cam when I'm sitting in the car, because it's blocked by the rear view mirror. It makes an audible sound when the car starts up, that lets me know if it's on. And if it ever stops recording for any reason (for example, if I've taken out the MicroSD card and forgot to put it back in), it will beep at me.
3M and tuck up it next to the rear view. If it doesn't have a bracket that you can slide it out of maybe use Velcro like the toll readers. I use 3M and route the wires up behind the headliner and inside the windshield pillar.
My dash cam suction cup likes to let go every once in a while too, usually when I get into colder weather.
I make sure to clean the window and inside of the cup real well and give it a little lick and stick it back. Low tech but it works until I get to freezing temps again. When this fails to work any longer I might consider a dab of aquarium silicone or similar. I'd rather not double-stick tape it to the windshield.
The best thing I did was hardware my dash cam in and secure the wire under the headliner. I cut some semi-rigid foam (closed cell foam from a computer box) into 1/4" x 1/4" strips 2-3" long and tuck them in after the wire. If the mount falls, the strip has enough grip and length (surface area) to suspend the camera so it doesn't fall and hit the dash.