Is "DUT_TOP" always the only portion of the design you care about code coverage on? Do you have other functional coverage components elsewhere in the design which you do not want to include in the UCDB file?
Depending on the answers to those questions, you could change your command in your script a bit, to read:
-coverage -voptargs="+cover=bcfst+/path/to/DUT_TOP" -do "coverage save -onexit gpex.ucdb"
You will have to replace "/path/to/DUT_TOP" which the actual design path of course, but this will then save code coverage for only this DU, as well as any functional coverage in the design (which would include whatever you have in "test_lib_pkg.sv".