I have kept/bred/raised veiled chameleons for over 12 years now. I've kept chameleons for over 20 years now. I live in an area where the winters are cold and the house is dry....and I have kept some of these chameleons in aquariums...just like many Europeans do. The aquariums usually had a screen lid and were long rather than tall. The cages that I keep them in now have screen lids and doors and the other 3 walls and floor are glass...and I find them hard to keep warm enough and humid enough in the winter. Keeping them as I do, most of my veiled females live to be 6 years old and the males usually live to be even older. BTW, I am not a vet.
I put the basking light at one end of the cage (which I see you have done) and the UVB tube runs the whole length of the cage. This provides a warm area and cooler areas in the cage and helps with the airflow. I leave the lights on 12 to 14 hours a day. Unless the room is very cold at night there is no need for heat on/in the cage at night.
The following information describes the way that I keep my chameleon and my own opinions about keeping veiled chameleons....there are other ways that work for people too which leads to the confusion. You must decide what to do for yourself. Be careful of just reading site after site on the internet...its hard for beginners to determine what information is good and what isn't...as you are already finding out. Here are a couple of sites with good information...
http://adcham.com/
http://www.chameleonnews.com/
IMHO the appropriate basking temperature/cage temperature is important because veiled chameleons need heat to warm up so that they can digest their food...thus use the nutrients that they are given.
I gutload my insects with an appropriate diet. I want the insects to be healthy and possibly contribute to what goes into my chameleons by looking after the insects properly. I use a wide variety or greens (dandelion greens, kale, collards, ROMAINE lettuce, endive, etc. NO CABBAGE, NO SPINACH), and veggies (sweet potatoes, squash, carrots, white potato, zucchini, etc.) to gutload them with. Here is a gutload that many people recommend too...
http://adcham.com/html/husbandry/gutload.html
I dust the insects with phosphorous-free calcium at most feedings because the insects have a poor ratio of calcium to phos. and this helps to even it out.
I use a vitamin powder twice a month that has a beta carotene source of vitamin A because it won't build up in the chameleon's system like preformed vitamin A can.
Because my chameleons rarely get direct sunlight and have to get their UVB from a tube light, I also dust with a vitamin D3/calcium powder twice a month. The light from the sun or the UVB bulb should not pass through glass or plastic. D3 from supplements can build up in a chameleon's system, so caution is needed not to overdo the D3 supplements.
I give my veileds some greens (same as listed above), veggies (except for white potato, same as listed above) and fruit (apple, pear, berries, melon, etc.) in a shallow dish in the cage since after they are mature, they are omnivorous....and it gives the insects something to eat while in the cage too.
I feed insects to my adult veileds every two or three days and I provide the greens, etc. every two or three days too. The wider the variety of insects you can use the better IMHO. Silkworms, superworms, butterworms, crickets and waxworms are usually available. I don't overdo the waxworms though.
I use no substrate with veiled chameleons because too many of the substrates can cause impaction (like calcisand). I don't want to even risk it.
I don't use plastic plants either...and the real ones that I use are well-washed (both sides of the leaves) and the soil covered with stones that are too big for the chameleon to ingest. The plants should be non-toxic too because veileds often/usually eat them.
I mist the chameleons and use a dripper. Its not advisable to let water stand on the floor of the cage because it aids in the growth of mold and bacteria.
You said..."He pooped once the day after we purchased him but has not pooped since"...if he eats he should poop. It might not be every day though. It might be that you have the temperatures in the basking area too low...but I think from the size of the cage and lightbulb you said you use, it shouldn't be too cold. It concerns me that you have used substrates in his cage due to the possibility of impaction.
I hope that your chameleon poops soon and that he will do well for you! He looks very healthy in the photos!