Here is what works for me. I wanted to make a unit for two people and keep it very simple, uncluttered, and easy to maintain. And yet have a furnace, beds, table, fridge, toilet, sink, and stove. I would have to say my unit is on the low side as far as availability of conveniences you might find in your home. On the other hand zouts M109 is set up to be the top of the line (Z is a very good friend of mine and both his unit and he himself are top notch.).
I live in cold country so being able to camp when it is around zero is a consideration for me. To winterize all I have to do is pull the pump lever all the way forward and it will drain totally. Then empty the water containers and I am done. By using only the containers inside the van I have no problem with freezing should it be below 32 degrees. Which will happen the way I use it. I can carry an extra 10 gallons of fresh water on the rear mud flaps if I need to. Our camping style is such that every few days we will pull into a campground with showers and other services and that takes care of those needs for us.
As far as propane I went with two 20 pound tanks. It is often hard to find an outfit to fill permanently attached tanks (at midnight) but easy to find a gas station etc. that has a exchange program for 20 pound tanks. In one of the pictures you can see where I put my two tanks. Another thing I did not want to have is stuff hanging on the outside of the van where it might get whacked as we are in the woods/mountains most of the time.
Zout mentioned that it does not matter what you make your unit have or look like. He is 100% correct. Everyone of us will want something different and that is great. We do these conversions based on what we want in a camper,what we have laying around and what we can afford. So look at others units and go for it. You can have a heck of a time by just tossing some stuff in the back of a M35A2 and taking off camping.