Building insulated dog kennel - Advice

He could need insulation to stop overheating in summer😎

Did it have Wifi?

Looks very good.

As regards a door, you only need to keep the wind off the dog( he will be fine unless it goes below 0 C).

You could try a wooden door, or some of that heavy duty plastic, like you see in warehouses to allow forklifts to drive through. Its about 8mm thick so very hardwearing unless you have a dog that chews through everything. Make it slightly narrower than the opening and split in two, vertically.