You can use the fused switchbox you show as others have said. I have used some variety of them in each of the rigs I have had and they are very convenient.
I also use a master battery cut-off switch and a large main fuse ahead of the box.
Then you can run circuits to the loads/lights/outlets and either let them be switched by the box or provide extra swithes if more convenient. It does seem a little much though in a tiny trailer that you would need more switches but that also depends on just how many switched loads you need.
On the other hand......you do not want to use ordinary solid conductor house wiring and you will want to run both a hot and ground wire to each load. Luckily twin conducter wiring is both available and inexpensive.
I don't want to sound too obnoxious is disagreeing here but there are definite reasons why automotive and marine wiring is stranded and not solid. Also different insulation types have widely different qualities than seems obvious from just using them. There are wires that are correct for mobile and marine use and ordinary Romex is not one of them. It is also very stiff and can be difficult to work with.
Regarding the grounds issue,our trailers more than others must rely on ground wiring to insure complete and safe grounding as there is often no clear path to a common ground just thru the trailer metal. In fiberglass trailers there is just not a common bonding to the frame as there is in other rigs. Also having been around the Playpac,it seems to have less going there than most. Most trailer lighting and electrical issues seem to arise as a direct result of poor/improper grounding.
It is no more difficult or expensive to do it right but it can really be an expensive problem not to.
All of the wiring and hardware to do this are available in the area and I use a wholesale place in the Westport area and the prices are even cery good.
I am working on my trailers over the weekend and am always happy to help.