When is an Exclusive Use Carpark not an Exclusive use Carpark?

Situation – open car spaces under the building one of which is legally allocated as exclusive use to my unit.  I am overseas and I don’t park a car in that space while I am away but have allowed a friend who looks after my unit to park a trailer there. It is a clean, registered trailer. 

I use the unit privately and lock down while away (or allow my agent to provide access to visiting friends).

The Body Corporate has issued a notice to remove the trailer.  They have also demanded that my agent register with the on-site manager every time he visits the unit.

I am of the opinion that this would be contrary to any by law.  I have requested a copy but they have not provided.

Any advice would be appreciated.