HOW TO MAKE A PUPPY INCUBATOR/BOX
This is how I have always made a homemade puppy box everytime I have had new babies. Made this way it acts as an incubator, and really does hold in the heat. It is also very hygenic and safe. In cold weather it really is a must. It can be thrown away once the pups outgrow it, and it is very cheap to make.
I also buy an electric heat pad, that has a removable washable fleece cover. They are readily available in most Chemists, and are actually sold as rheumatic heating pads for people to use to apply heat to their necks etc. I rang the manufacturer, listed on the box, and got spare fleece covers. This means I can remove and wash them daily. It has a two setting heat adjuster, which can be turned higher during the night. It can of course be turned off if it gets to hot. It measures 18" long by 12" wide.
I try to get a sturdy cardboard box about the same size, or just slightly larger, that is about tweleve inches high. If your mother chihuahua is larger, then you would of course get a taller box.
First I cut an opening in the front, depending on the size of Mum. As small as possible, enabling her to get in and out of the box when she wants too. I use paper masking tape to cover where I have cut the box, so that there are no sharp bits that puppies could hurt themselves on. I then use masking tape on any corners inside the box. I then layer the bottom of the box with several newspapers.
Next I cut an even opening in a bottom corner at the side, towards the back of the box through which I can put the electric lead of the heating pad, which side depends on where your electric socket is that you need to put the plug into. Next I place the heating pad in the box, thread the lead through, and making sure I can still lift the pad to change the covers, I tape down the hole I have cut, both inside and outside the box. Next I cut off the top flaps, and make a roof out of newspaper, I use several thickness sheets of newspaper for the roof, which I tape down with a good quality masking tape. Once this is done, I then get either a softer bit of cardboard, or as I have used this time, a strong large brown envelope folded in half. This should be flexible enough for the mum to be able to push down on entering the box. I then tape this to the bottom of the front opening, and extend up by about three inches. The photos below will explain all this for you. The idea of this extra piece of covering is to stop the puppies being able to get out as they start to grow, yet soft enough for mum to lean on as she gets in and out. Once they reach the age of being able to climb over the top of this extra piece I remove it, so that they can then get in and out of the box, without falling onto the tops of their heads.
Once this is made, I place the whole thing into a corner of my large wooden whelping box, hubby then threads the electric cable through the bottom at the back, so that I can then plug the heating pad in, and have the controls on the outside. In my wooden pen I put a layer of paper, and I also put a seperate fleece blanket on the floor so that mum is able to get out of the heated box and lay seperate from the pups if she so wishes. I find they do like to do this and go back in when they have cooled down and the pups need them. I also put a water container on the front wire of the outside wooden pen, so that mum always has fresh water available. This also helps to keep the air moist around the pups. If you do not have a large wooden whelping pen, then the box can just as easily be used in a playpen. At the back of the cardboard box I securely tape a thermometer. This enables me to peek in to see that the temperature inside the box is correct, without disturbing the puppies.
Below are the photos, starting with what the box looks like before you add the extra front bit. The second photo shows the fleece heating pad. The next shows how the electric cord is placed safely through the box. The last photo shows the finished item, with the extra removable front.