If he did "shrink wrap" Susan's body, he would have needed working room. But that wouldn't explain why the carpet was wet. One would think, if he planned Susan's murder in advance and it involved shrink wrap, he would have used it to wrap around her face when she was sleeping to smother her and that there wouldn't be any blood. However, there is the possibility that he dragged her out into the living room to finish wrapping her and that her bladder or bowels released, thus explaining the reason for the large wet spot resulting from using the carpet cleaner, a cleaner which a reliable source told me they owned for many years.
I really don't think, if he murdered Susan, that it was premeditated due to the strange story he told upon his return from the camping trip. (Perhaps he was gone way longer than he planned and never dreamed he would have to come up with an explanation to anyone about why he was gone from the home. Perhaps he planned on returning and going to work as usual but ran into complications. The fact he took the boys with him indicates to me that Susan was not home to take care of them.)
There is also the possibility that he left so someone else could do the deed when he left to take the boy's sledding at around 5:30. But, nobody reports seeing anyone go to the house during that time.
There is also the possibility that he brought someone back with him when he came back from the sledding trip. However, I would hope the person who interviewed the five-year-old would have asked if someone was with them.
I would think using the shrink wrap in the house to wrap Susan's body would have caused microscopic dust from the shrink wrap to float around the entire house which would have been discovered after the forensics were analyzed. Perhaps nobody told law enforcement about the shrink wrap until very recently and they are in the process of running additional tests.
Regardless, prosecuting someone for murder without a body is not something that is done a lot and is a very risky move on the part of a prosecutor. People keep hollering because JP hasn't been arrested yet while failing to realize that preparing a case, (against a suspect where there is no proof the person they are being charged with murdering is absolutely and without a shadow of a doubt DEAD), is a huge responsibility and risk. We all know that people can't be tried for the same crime twice. The fact JP hasn't been arrested is because Susan's body has not been found, not necessarily because the district attorney doesn't have proof JP murdered Susan. They are waiting in hope that her body will be found, in my opinion.