My reply and general thoughts:
I am sorry to hear about your troubles and understand your frustration.
You are correct that the move is stressful for your cat. The first thing to mention is the importance of ruling out an underlying medical condition, such as an infection, partial urethral obstruction or other disease process.
Stress can cause urinary tract medical problems. Since he is also defecating out of the box, there is a good chance that it is a behavior problem, but it is important to always be mindful of a medical problem causing inappropriate elimination.
He may view the sun room as "outside" if the new house is larger than the first. Cats will eliminate out of the box to 'claim' the space as their own (with their scent), too.
Sticking his nose in the urine, yelling, or otherwise punishing your cat will not stop this behavior and likely only create additional problems. It may also cause your cat to seek out more "hidden" places in which to eliminate.
Quick tips to help get your cat back to the box:
1) Confine him to a small room until he feels safe, secure, comfortable. The room should be inviting, warm, etc. Not a cold, uncarpeted space without furniture or cat-friendly places to sleep/feel comfortable. Gradually expand his 'territory'. You may need to add more than one litter box. At least two would be preferable, more if you have more than one cat.
2) Offer a fresh litter box (or preferably, boxes) with unscented, clean litter. There are many types of litter available. If you are unsure what your cat would prefer, offer a few choices, keeping the regular litter and litter box in place. As a general rule, stay away from scented choices. Those scented litters are ridiculously strong to my nose, and cats can smell 20X better than humans!
3) Clean the litter box frequently. Daily scooping is preferable. Washing the litter box with a non-toxic, non-scented, non-ammonia cleanser once a month is also helpful.
4) There are also specialty products to make the litter box more attractive. I attended a conference on feline medicine recently, and here are some recommendations from the presenter, Hazel Carney, DVM, MS, DABVP:
- Zero Odor Pet® - for cleaning the litter box
- Cat Attract Litter Additive
- Feliway spray or room diffuser - learn more about Feliway here.
5) The food and water dishes should be placed as far away from the box as possible.
Tips to discourage inappropriate elimination:
1) If he is eliminating in one specific area, place something non-toxic but aversive, like aluminum foil on the floor. Another tactic is to use a carpet protector with the "spikes" up. This is a gentle way to discourage your cat from using the spot, and also works if you do not want the pet on the furniture.
2) Putting food and water dishes in the troublesome area often serves as a natural deterrent -- cats do not like to eat in the toilet area. I do not recommend adding a litter box to the area, this may create confusion.
3) Clean the litter boxes often and praise/pet him for good behavior.
4) As hard as it may be, "ignore" and downplay the inappropriate elimination acts.
5) Clean accidents up with any of the many good, pet-safe enzyme-based odor eliminators and cleaners available on the market (see above).
Related links from Franny Syufy, Guide to Cats:
Litter Box Essentials - lots of helpful links on many litter box topics and issues, including litter and litter box product reviews.
Read all of the posts in this discussion and add in your thoughts.