I agree with some of the others that if you're going to use it on a septic system don't put in an RV toilet or holding tank. Plumb it directly to your sewer just like in a sticks and bricks application. If you install an RV appliance and holding tank you will need to hold waste materials until the holding tank is nearly full before opening up a valve to dump the tank into the septic system. Not all THAT much of a problem but all unnecessary if you plumb directly to the sewer.
The only DOWN side to this would be you no longer have an RV as you've turned it into a cabin. Would not be suitable for RV use where it travels from place to place.
Good luck / Skip
