Trivial = Expensive
I am sure that threats like this are 'trivial' to defeat - the problem is that you now have 4 sat nav receivers, and they have to be linked (so now we have a new vector for introducing bugs). Meanwhile the 'baddies' will have moved on, found something else - (I suggest a constellation of 4 drones in formation 'simulating' a real sat nav constellation - done right I think that could be made indistinguishable from reality, as they could drift across the sky in appropriate spots on a line of sight between target vehicle and the real satellite. You could have another set of drones spoofing the cell phone towers. Having watched several realistic documentaries about such impossible missions, all that you need is a bright 16 year old hacker, a handful of off the shelf hardware, sticky back plastic and a pizza.