Nipuna,
My mom also getting this permit so I gathered some info.
Your uncle cannot transfer the Book to your name untill 5 years. hence Book it self will be keep by the Import/Export Ministry untill the 5 years time.
Government will put special mark on the registration number plates so it can be Identify any where.
Legislation clearly said that the Owner of the car cannot rent,sell, or give it to any one. If you got cought by doing that your uncle might have to pay the whole tax.
But during the past years people have sell there permits and nothing happens to them.(Not that I knw)
Customs may check the vehicle once a while.( So far it never happens)
Cheers,
DCL