Do you think I need to add any insulation to the sides and bottom if I go ahead and add the dirt in both areas? As I mentioned, the top has 2 layers of wood with insulation in between.
I think this sounds just fine....I would just keep an eye on his habits when the weather becomes scorching and also plan to have a little mister/sprinkler that you can drop in or near his yard space to allow a cool off and fun in the sun in the water---they really do enjoy the water/sprinkler time.
I have an older CDT (we call him Old Man) and he has a day yard that he enjoys from early am to night time....I have cinder blocks for the walls (filled with dirt for insulation) and the bottom is the earth directly and a double wood roof with an old road sign that is under the wood in the event of a down pour his hide inside remains dry....well, I have tried a variety of hides for him (as he does not burrow) and this old rickety thrown together hide has been his fav....I have tied a regular ole thermometer to a string and tossed it down into their hides/burrows and just left it there for about and hour or so and then pulled it back out to see the temp (albeit it is not a scientific method...lol) but it gives me a secure enough idea ...so I would recommend doing that or your own version of obtaining an idea of the temp....
I am happy to hear that you found the links helpful and useful....