Gut mains at low tension will defeat the purpose of gut mains/copoly crosses hybrid. Gut mains strung too loose will stretch sideways too far and fail to snap back in time to provide the extra spin this setup is known for. Instead, you'll just get a very high rebound angle and poor control. You're better off picking the least stiff copoly you can find for the crosses and stringing tighter rather than looser.
Sub-50 tensions really only work with full copoly and kevlar/copoly hybrids.
Copoly mains with gut crosses might be Ok, but I would'nt even try it myself.