Many times I have been asked to secure a up and over door .. If you think like a criminal then the answers are obvious ..and believe it or not, the simple things are the best.
If you asked me to get through an u/o door (assuming it's metal) my first choice of tool would be a spade or a crowbar. I'm afraid I have fitted plenty of the locks that Buenchico has shown in the link and if the burglar has a lever, they will just prise the door away from the frame and the bolt pops out of the sleeve within seconds. The metal doors tend to be thin sheet metal and are fairly useless as far as security is concerned.
Think more along the lines of 3 lengths of 4" x 2" across the back of the door extending as far as the frame will allow. You would then need to fashion steel brackets that the wood can be dropped into.
As a belt and braces approach .. drill clearance holes through the battens into the frame while the wood is in place. Get some 5" bolts and just pop them in the holes...even that will keep me out.
Top it off with 2 eye bolts and a padlock at each corner and you have Fort Knox. I'm guessing you have anchor bolts drilled into the floor for the chassis lock ?
Not to forget .. two 5 lever mortice locks in the rear door fitted 20" up and 20" down.
If you are anything like my neighbour who has 3 bikes .. dry, wet and a mx. you will want to protect your investment.
The easiest door to open is a partially opened door .. so your challenge is to stop that door being partially opened in the first place.
The thing is .. if someone comes prepared .. you wont stop them. But a number of simple hidden measures, may well put them off.