The first thing that I notice when looking at your enclosure is how empty and two-dimensional it is(only one plane).
What options does your animal have, as far as movement goes? It can go back and forth along the enclosure floor... that's about it. Look at how much volume is going to waste in that enclosure. The animal has virtually no ability to climb(something that collards will certainly do), or move anywhere but on the ground. There isn't much of a gradient in temperature levels available to the animal either, as you are neglecting to offer any way of allowing the animal to pursue greater heights/vertical zonation, where temps will vary with height.
I used to build enclosures for my captives similar to yours, although I did offer more usable objects and varying conditions within the enclosure, when I realized(with a little help from some of my European herp keeper buddies), how much a fool I've been for not recognizing valuable cage space that was sitting right in front of my eyes the whole time!! The walls!!!
By making the walls usable- by covering it with some type of climbable material, you will increase the total square footage of space available for your animal to use by at least five-fold. This also opens up and allows for three dimensional range of motion, as opposed to your current situation which is only two dimensioned..
I would also allow for multiple conditions within your enclosure, that the animal can use at its own leisure.. Some of the more important 'variations' being areas of different humidity levels-perhaps a couple of damp hides, as well as some dry hides, cool hides, hot hides, etc...
The more choices you allow your captive to make, the healthier and better off it will be. Also try to think 3 dimensionally... Cage walls are prime real estate which go to waste in 99% of people's enclosures.. Nothing is static in the wild, within any habitat there are microhabitats, and within each microhabitat there are micro-micro habitats(hahaha). Animals in the wild are exposed to and have access to these many different conditions, whether they be climatic conditions, or conditions that the animals seek out for their best interest, such as a damp, cool burrow, or beneath moist leaves, etc..
I hope this helps a bit, the key point to consider, in my opinion, is to offer your animal as many choices and available options/resources as possible within your enclosure's limits. Take a good look at what these animals are exposed to in the wild, how they behave in the wild, what they use in the wild... and apply that towards providing for your captive...
Take care, have a wonderful day! Best of luck to you.
Bob
*here's a link to a DIY article that I wrote up on maximization of cage space, that you might find interesting/useful. While it bears emphasis towards the tree monitors that I keep, this methodology and technique can be applie to virtually any other lizard species, even 'terrestrial' species- which will do a fair amount of climbing in the wild.. :
Maximization of Useable Cage Space
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Treemonitors.com