We also looked at this trailer and had it in our head we would do a top entry litter box in the bathroom between the toilet and counter. We had gone as far as measuring and it would fit. Mats to catch litter would have gone in front of it. We honestly thought it was an awesome bathroom to have everyone do their business in one spot, away from the living area.
We didnt end up with that trailer, and in our 240ml it is under the bed. I removed one side of the under bed wall (fully intact, so I can just put it back if we ever sell), and added a removable wall in the middle under the bed. Now one side is litter box and one side is storage, completely separate.
Considered using the front storage, but didnt want to cut a permanent hole, plus we use that storage. People have done cool stuff with that though if willing to make a hole.