If there is enough room on your stand, you can make a little DIY and put black plastic sheet against the tank. Make it taller than your installation so you can then put a fifth sheet at the top. Your turtle will be completely isolated !
I do recommend not covering the top entirely so your tank won't get too hot ! I had to cover my tank for a night once and did so with a towel. In the morning it was overheating. So maybe leave a space uncovered, where your turtle don't sleep