I thought about this for a while. The choices were many.
Purchase a set of Westy cabinets from a european source. Very expensive, lengthy lead time. Way beyond the level of this quick weekender conversion.
Install a piece of household quality furniture. Difficult to find a 30” piece, and most household furniture wastes a lot of potential storage space.
Build something yourself. It will never be high quality, but it would be inexpensive and fast.
Find some used Westy cabinets. Fairly rare, and not that cheap.
Of course we chose option 3. Since the preference would be for a rustic look anyway, it was 2×4 and plywood time. The key issue was establishing a secure attachment point for the cabinet. The long wall has an interior sheet metal skin. A stud and some sheet metal screws created a level and secure starting point. The rest flowed fairly easily. The new plywood floor helped, when combined with some liquid nails and a few drywall screws. The shore power 110 outlet was mounted under the counter top toward the rear seat. The main theme was whatever was on sale at Home Depot. 1/4 plywood and a blemished Formica counter top. A salad bowl sink, a plastic storage drawer unit, 6 gallon water storage containers, and a vacuum-powered faucet.
The end result is basic and certainly rustic. However, it is completely functional for the intended purpose.