....he keeps trying to seed areas in the house, and once you let a crap-pile get established somewhere it grows.
Yes, what a good description.
I have tried the throwing away surreptitiously - it works pretty well. What's more DH doesn't know because he can never lay hands on his crap valuable items anyway.
Storage space - we tried that. What stuff is getting stored? Well, typically boxes of vitally important information notes from a course he took and passed/failed twenty years ago. Not just a neat folder of notes, or marked essays, but all those pages of rough workings and crossings out! And other such stuff! What a waste of money.
Does anyone remember that programme Life Laundry with Dawna Walters back in 2002-4? DH had a bit of an epiphany when watching that. He saw Dawna sort out someone whose child had no bedroom to sleep in, and was camping out in a space on the landing, because the bedroom was full of the husband's crap. Well, my DH was suitably chastened because he recognised himself. (DW was good because she tried to understand the psychology of the hoarder.) Long term, the lessons learned from Dawna didn't work, and on those rare occasions now when we get a freshly cleaned space it's not seen as a place to be enjoyed and lived in, but a blank space crying out for the installion of more crap.
My parents used to have the same problem. My mother used to tell my father that when she was gone he could have a lovely time throwing stuff out to his heart's content. The trouble was she outlived him, and my brother, SIL and I had to slog through all the stuff after she was gone. In the end we gave up and got a house clearer in.
It's an ongoing battle, I tell you.