Ugh, that is a crazy story, and I'm sorry you're having to live through it. Good that the testicular cancer is manageable at least.
With the signet ring cell adenocarcinoma, it's just hard to know what to say. It's rare enough (<1% of colorectal cancers) that there may not be anyone here who's had experience with it.
I'm going to try to comment, though I'm just giving an amateur opinion going off my limited knowledge of non-SRCC colorectal cancer.
First, I wouldn't be especially distressed about not finding survivor stories on SRCC. It's rare enough that there aren't many stories at all. You're a trailblazer (lucky you
) So you're going to have to show us what an SRCC survivor story looks like.
Second, it sounds like the only metastases your husband has are in the peritoneum? If that's true, maybe he would be a candidate for Hyperthermic intraperitoneal chemotherapy (HIPEC)? I don't know much about that, but others here probably do. Here's an article on it in the UK. http://www.nationalmesotheliomahelpline ... sufferers/
It's controversial, and the Royal Marsden may not do it, so maybe it's worth a second opinion at a place that does.
That's all I can think of for now.