I suggest you scrap the high heat Sun lamp and get two or even three lower wattage heat/uvb lamps. My biggest mistake with my tegu was using one lamp so he had to hunch up under it. If you have two or more lower heat lamps they can stretch out more and it doesnt get those super hot spots but more even heat over its entire body(ours was a solid four foot male).
We had a small room that our tegu occupied and we kept a big tub(6ft long) filled with dirt and a side entrance so he could go in and bury himself. It had a warm end and cool end(using under hide heat).
We also had a section with cinder blocks and heat/UVB lamps (the cinder blocks help radiate the heat). He would stretch out under that.
Seriously they dont have the same requirements as Savannah monitors(who need much higher heat and humidity).
Argentina is not a hot nor that humid of a country. But they do need a certain amount of humidity.
Tegus still need hot spots above 100 deg to digest properly and regulate temps. Having one lamp as a primary source of heat/UV with a MVB is just fine as long as the dome is big enough to disperse the heat.