I use a NanoVault when I need to disarm prior to going in somewhere that is restricted, then rearm when I get back in the car...it's good for short term storage in vehicles.
I put a Snapsafe combo lockbox XL (10x7x2) under my drivers seat cable locked to the seat frame. Had to add some velcro hook to the bottom of it to keep it sliding forward when braking. It's handy, but I don't have any illusions that it's super secure. I've used it a couple times for short duration storage requirements. I try to park where a break-in would be unlikely, then rely on the car alarm as a secondary security measure, and the lockbox as the third. I'd love to put a really big heavy duty safe that's too big and heavy to run off with in the back of my SUV, but access to the spare is also back there.
I have a Loctote bag that I use when I need to lock my gun in the car. I use a small key lock rather than the combo that came with it. I lock the bag to the seat frame.
I have always been of the mindset that the best theft deterrent is concealment. As you said, any security measure can be beaten by a tenacious thief with enough time. When it comes to my vehicles, the tried and true best practice for avoiding break-ins has been to keep them exceptionally clean inside and out. Psychologically speaking, it makes sense that a (presumably experienced) thief will opt for the easiest target available given the choice. If your car appears to be a treasure trove of goodies, complete with a little of everything, then it is more likely to be targeted. I would feel better leaving my firearm under the seat of a spotless car than locking it in a safe within one that presents a more appealing target. On a secondary note, vehicle alarms have come a long ways in recent years. Mine is positively obnoxious; even if I am not nearby, SOMEONE will come running if it goes off.
I had a tuffy center console vault in my old FJ, along with wooden storage drawers in the trunk. my Truck locked, with an alarm, in a fenced lot with security is already a better security than a cheap gun box. So with my new SUV, I went with the hidden route: don't mind this, just a jack box Nope! sneaky rifle and have to finish my second/3rd row that folds up and reveals this!
Quick, easy, and reasonably secure.... Pass one handcuff through the trigger guard and the other cuff to a seat rail that's bolted to the floor. The pistol will be under the seat and out of view. I suppose if you want the double deal, you could pass both cuffs through the trigger guard and seat rail. Just remember that whatever you bound so you also set free.....take it easy on yourself. In case you should run up on some old guy on his knees, saying Hail Mary's at his open car door...... Remember what they say about old guys and don't mess with him.
I have a Bulldog personal safe like this one: https://www.bulldogcases.com/product/personal-car-vault-with-mounting-bracket/ It will deter a casual thief, I suppose, and that's all I really expect of it. I picked it up at a local Cabela's a few years ago just before taking a long driving trip from state to state. Its primary attributes are convenience and portability.
I have a long gun under my back seat with a cable wrapped around the seat post, through the mag well, and secured with a padlock. I live a pretty safe area and am comfortable with the level of security that provides... Sent from my Pixel 2 using Tapatalk