It would be great if you could have different levels of basking branches under the basking light with the closest one no more than 6" from bulb to avoid burns. I would try a 60 watt bulb. That is a large enclosure so if you put the basking bulb to one side and cover the back and side of the enclosure, it should warm up that area. They cham would have to option to bask at whatever temp he needs.