Hi,
Is leaving one side open for viewing important to you?
If not then completely covering all the sides/bottom and probably most of the top with reflectix or cork sheeting might help keep the temps more stable but it's always going to be tricky to heat that volume I think.
I used to use a 5 foot by 2 x 2 wooden vivarium with a 700watt ceramic heater (on a thermostat of course) and used a large humid hide in addition to the regular ones to try and help with shedding.
It cost an absolute fortune to run and , to be honest, I don't think I will ever try and use it for anything again as the best you can manage is a compromise and bodge/ make do situation.
Just my 2c.
dr del