As others have said, you need to use flush lever to fill bowl with water before using. On some models you press the lever down part way and others you lift up on lever to fill bowl. In either case you should keep water in bowl between uses. This will help keep odors and gases from escaping as well as keep seals from drying out. It has also been mentioned that the dump valve should be kept closed until the holding tank is close to full (2/3 or more). At that point he just needs to go out an pull the lever to dump black tank. After dumping and closing valve add a few gallons of water through toilet into tank. Toilet paper is not a problem.
We did the same thing with our trailer for our daughter while she attended grad school. Worked out really well for her and us both. Once she got settled she preferred it to both the dorms and apartment she had been in previously. In our case her mother also was traveling to the area every month or two for business and so it gave her a place to stay as well. When I visited I would rinse the tanks and check propane etc. for her. Fortunately it was only a couple of hours away and my schedule was pretty flexible.