You need to declare it in Init method:
Scripter.DefineClass(TTestRecWrapper);
and then use TTestRecWrapper.Create in your script.
But if you are using Delphi XE2 and newer, you can simply use
Scripter.DefineRecordByRtti(TTestRec);
You need to declare it in Init method:
Scripter.DefineClass(TTestRecWrapper);
Scripter.DefineRecordByRtti(TTestRec);