Maybe try a 15qt tub: not huge but not too small (I can put two hides, water dish, and thermometer in those).

Also how often are you trying to feed? Give him 5-7 days in between offering feeders: offering too much could stress him out and make him not want to eat. Have you tried live or just f/t? Was the seller feeding him live or f/t?

Can you explain your setup more? Ambient temps, hot and cold side temps, how you're measuring them, etc