16ACE27 had it right: it is under the bed slide. I haven't figured out how to remove the drawer that is in the way so I went with Coveman2's suggestion of looking behind the exterior shower assembly. Lo and behold, that's where it is.
It appears a valve was closed (likely during winterizing last fall) that prevented water from getting to the pump. I opened the valve and all is well.
Well, almost. Two of the shower assembly mounting screws are stripped so I'll need to fix those holes. Found plenty of sawdust, metal shavings, and loose screws in the space where the pump is located, so some additional cleaning is in order.
Photo gallery:
https://photos.app.goo.gl/uPzvkPJwDJqj8C886