Several moves and one wife ago I used the guest bath. The part that was the hardest was blacking-out the room. I solved that by making the room permanently dark. I blocked the window from the outside and painted it to match the house. I then used a liberal amount of weather stripping and pipe insulation (for the bottom of the door) to black the door area. Everything needed was on a rolling cart stored in a closet. Set up was less than 30 minutes including mixing chems. Tear-down was a little longer and usually done the next day.
When I found myself single, and in an apartment with one bathroom, I was content with leaving as much stuff in the bathroom as possible.
I’ve had two Drs in small (cramped) bathrooms in the past two housed that were rented. Now we own a house and in the next few months will start on a permanent DR.