In actual fact,the AXN would fit in a small car without taking the wings off.It's only 4ft span,and I don't know of any small car that has less than 4ft.width across the inside of the car.You could also fit it in with the wings pointing fore-aft,making it shorter still.
What you could do,string a couple of bungees between the grab handles or coat hooks,and slide the axn in above them,with the tail pointing down.
You could certainly make the tail removable,but such fittings will add weight,and weight is the enemy!
If there's absolutely no other way,fit wooden dowels just below the tails normal position,and use rubber bands to hold the tail on.check interference with the elevator pushrods movement.
I would NOT advise magnets or velcro to hold on the wings or tail.If you do,your AXN will have a short life.
Making the wings removable is a whole different ballgame.I would drill holes through the bottom(or top) of the fuselage,with the wing on,ensuring that you do not hit the spars,or electronic wires,etc.
Then I would epoxy internal threaded fittings in the wings,and use a nylon bolt through the top or bottom of the fuse to hold the wings in place.You would need to add some sort of strengthening around the holes,again adding unwanted weight,but I believe that's vital if you're going to be removing the wings after every flying session.
As far as a box goes,this would still be pretty big,as the AXN's fuse isn't that much shorter than the wing span.
I suppose you could add a roof rack,but that'll cost you an arm and a leg.Your petrol consumption will also go through the roof.What sort of car is it?Hatchback,sedan?
If that all fails,what about a small trailer?Then again,that would probably cost you more than buying a bigger car
.Hope that gave you some food for thought.