When I first read this thread I thought you meant you were crate training using an actual crate! lol, but you actually mean a puppy pen?

I think the advice that has been offered so far is fab, so can't really offer any other advice on how to make him feel comfortable in his pen.

But I will mention this... you said you start work again in 3 - 4 weeks? and he will be on his own during the day? well, you really need to start getting him used to being on his own for short periods of time during the day. If you start being in with him pretty much all the time for the next 3 - 4 weeks... you are going to have difficulties leaving him alone when it's time for you to go back to work. He will probably whine and do what most pups do when they aren't used to being left alone.

I am sure someone with alot more experience can offer you advice on how to get him used to being alone without getting bored/stressed/upset or lonely, so to prevent seperation anxiety problems later on.

Good luck.