Hi Nancy, this is Linda, a vet with 10 years of clinical experience.
I am so sorry to hear about this issue.
Oftentimess, not using the tray is linked to anxiety. You say he does it when things bother him, so this makes sense. He is not acting out or doing it as a 'protest', he is simply stressed.
Ideally, we'd avoid those situations we know cause him stress when possible.
To reduce stress in general, we should start some daily calming supplements in his food and can also use a pheromone plug in.
The rule of thumb is that there should be one tray per cat and one extra. So there should be 2 right now if he is the only one.
Trays need to be in areas of the home with low foot traffic, where he has privacy.
Cats are often incredibly fussy and won't use a tray because it is dirty , so keeping the trays as clean as possible will help.
If you cannot do this, I'd invest in a self cleaning tray.
Some cats have a litter preference, so the answer can be as simple as changing the type of litter you use.
Ensure he has all of his own resources and plenty of spaces he can go to be alone when needed.
This means a food and water bowl that are not close to each other or to the litter tray, a cat tree, a scratching post, a window from which she can see the outside world, toys, cat nip, food puzzles etc.
All 'accidents' should be promptly cleaned with an enzymatic cleaner, to eliminate the odour and prevent re-soiling.
We should never tell him off for accidents, as this increases anxiety and makes things worse.
With regards the vent, we can use a sponge on a handle to remove excess urine, clean the area and then use an enzymatic cleaner.
For further reading, this resource is very good:
Finally, if not already done, a vet check and urine analysis is sensible to rule out an underlyiong medical cause for this, such as a UTI or urinary crystals.