What I can't believe is that you haven't even tried something like Feliway because he doesn't look stressed. I'm pretty sure from what you've said though that he's developed a negative association that using the litter tray will make him feel bad, if you haven't already you should try a new tray or better still new trays in different places and with multiple litters, and a Feliway certainly worth a try. Also a behavioural expert could be worth a try? Although it sounds like you're dead set on getting rid of him now which I find surprising if you are as attached as you say
Well, I expected the thinly veiled judgmental post to occur sooner or later.
To make things a bit clearer for others, which is probably needed:
Using a litter tray: Not a single problem, never has been.
The bath thing: When he had one of his visits to the vets, something got wrapped up, stretched and very inflamed (makes me wince writing it). This is the real shock that he had. He was on painkillers, inti-inflams etc and to prevent litter particles getting in there during his healing persiod (about 6 weeks), we allowed him to use just paper, or even just the empty tray. This also gave the benefit of seeing how many crystals he was getting out of his system by himself. Now, unsurprisingly, it appears he associates the smooth bath surface, with a huge empty litter tray.
Dealt with by keeping bathroom door closed.
The duvet thing: When he was a kitten, he did a whoopsie on the bed. No big deal; he never did it again. Until after all the crystal business. He won't do it if you're in bed, but if you leave that bedroom door open when you're out, expect to find a present on the duvet.
Dealt with by keeping the bedroom door closed.
Carpet wetting: He's only done it the once; not sure why. It could be because there was a thunderstorm that night, but I'm don't know.
The problem is, I cannot give him a quality home now due to being only me here, and I now spend a lot of time away, so all he will see is a cat-sitter for half an hour, and the above 'features' to his personality are making rehoming a difficulty.
I'm starting to realise that any rehoming charities are not interested unless the cat is abandoned, or with kittens.
He's not a lost cause, all he needs is someone that can keep the bedroom & bathroom doors closed and feed him Hills C/D wet, in morning and at night.
EDIT: D_K good luck for kitty - that Hills C/D stuff is miracle-food; Pet-supermarket is usually the best source if you end up on that route - they deliver by DPD as well which makes things easier.