Not sure how big of a space he is in. Perhaps using the large rubbermaids that go under the bed, and set them up like some folks do for the litter boxes? Put down wood pellets, then put a screen over it so the urine drains away from him and then cover in hay for softness. It might be a bit messy with using a lot of hay, but you don’t have to worry a bout him chewing or ingesting funky materials. If it’s a large space you may need to use more than one, or if it’s mostly just where he sleeps, set up that spot that way.
there are also those mats meant for dog kennels that are like grates as well, so liquid would flow through them. Some of those can be huge and then cut to size for his cage, if he’s in a big pen this might be helpful. You could then line under them with puppy pads and he wouldn’t be able to get to them.
if he starts to get urine burns, I used calendula cream on our old skunk and it worked wonders on keeping it protected between washings.