Closed loop systems typically run at about 10-20 psi and have a pressure relief valve set at 50 psi, so your hose idea should theoretically work fine since car radiators typically run around 15 psi.
Solar Hot Water for Cold Climates: Closed Loop Antifreeze System Components
It would be a little more costly but you could always put on copper unions. This would definitely hold the pressure and still allow you to disconnect the panels if needed.