Before you go through a lot of planning, work, and expense, you should consider a couple of things. A traditional marine MSD is not always the best option, especially for smaller boats. A 10 gallon tank likely won't get you a week's worth for two people, so you will need ready access to a pump out station. Never use a metal holding tank, as urine is acidic and will corrode metal. As a part of designing a new system, you should include a robust ventilation system, which will encourage aerobic bacteria, the kind that doesn't generate the gasses that permeate many boat's interiors. Odor proof hoses aren't. It would be time well spent to read the wealth of information on the web about how to design a good MSD, don't rely on what boat builders do, they are mostly incorrect.
Traditional marine MSD systems are not something thought up by sailors, they were mandated (with good reason) by environmental governing bodies and designed mostly in the likeness of residential sewage systems. Boats generally don't have the capacity for onboard sewage treatment facilities, so most rely on carrying the waste around until it can be transferred to a land-based treatment plant.
Another option is composting. There have been some really good conversations here about this solution. Many boaters simply do not understand that composting is not something complicated and untested. It is essentially what bears do in the woods. You can design your own system with a 5 gallon bucket and some composting material. I chose to step up from the bucket solution because my wife has an aversion to primitive bathrooms, and we expect to be spending a lot of time on the boat so I considered it a worthy investment. It is still less expensive than traditional marine MSD systems. Another sometimes overlooked benefit of a composting system is that you eliminate two extra holes in the hull below the water line, and an extra hole in the deck for the pump out.
I am in the process of installing a C-Head churn-less shorty model into my 23 pilot house. It is replacing a OE Jabsco with 7 gallon tank. I am not criticizing Hutchins, as they are unparalleled in almost every aspect of their design, and I am sure the system installed was at the request of the PO. I have had a conversation with Gerry about composting head options, and he said he has considered it for the 23 pilot house but the early systems were too big to fit. As soon as I complete my install, I will provide the details to all.
I chose the churn-less model because I can get about two weeks of use for my wife and I and the emptying process is much simpler. If you need longer service per emptying, there are the standard height and churn models. So far my installation couldn't have been simpler or smoother and the results look really good. The installation is pretty much "just sit it in place" and secure it if needed. Although it was provided with my model, Sandy suggested that venting may not be necessary, so I will go with that for the time being. C-Head has done a great job of providing solutions for any requirement and installation configuration. Sandy at C-Head is super helpful and straight forward. Visit the website, and call Sandy with questions. http://www.c-head.com/
P.S. I now have a Jabsco head sitting on my dock, and hope the neighborhood kids don't think it's for them.