I agree with Puddn. If there is a by-law permitting this type of storage then your neighbour cannot object to you installing it.
Is there a condition in the by-law about getting DA approval? If not then just comply with any conditions that are included in the by-law and go ahead and install the storage unit.
The OC may own the dividing line as they are probably responsible for maintaining (i.e. re painting it) it so perhaps you would be safer keeping the unit within your car space. This could be something about which you check with your committee or your SM.