What would cause a male cat to pee outside of the litter box?

He is 13 years old (neutered). He is living with another female (same age/spayed).

First time that it happened, he peed on a camping tent that we had used. It was left in the hallway (not assembled of course, but all of it’s parts were laying on the floor). Next time, he peed on a few camping sleep bags. That happened a month later.

A few months later, another male cat peed a little in the bathroom when he had to have a flee bath (poor kitty freaked out because of the water). The mess was cleaned up well, but the 13 year old male ended up peeing over that pee. So, the bathroom door was shut after that.

Fast forward to last night (this is after a good 8 months after the last incident), a brand new camping sleeping bag was used (it was a cold night and the power went out). He slept on that sleeping bag with my partner. Through the night, he got up, jumped onto the bedroom dresser and peed on a pile of clothes.

Is it the camping gear??? Water repellent something or other that’s setting him off? Could it be his age (possibly a urinary tract infection)? My partner hasn’t been home that much and she is notorious for not keeping the litter boxes clean, could it be that? His box too dirty??