Re: How big a holding tank vs. camping
The 8 gallon holding tank I had in my Norsea was the biggest I could get into the space available. Filled up way too fast and was waa-a-y too much trouble. It was the "controlling" system on the boat when in inland waters. When poop - not potable water/not fuel/not food/not beer and rum and coffee - becomes controlling then a solution is needed.
So we starting using Wag Bags. Better...but still a PITA.
My C-head was the solution and I will never go back to a holding tank. Not much greater effort than the toilet on the farm. Still have to clean it. Don't have to use Rid-x for the septic. Never have to wiggle the flush lever when the valve starts to leak. Never have to adjust the lever-to-chain connection when the throw is too small or too great for efficient flushing. Never have to replace the "guts" of the tank because of leaks or corrosion of internal parts. Never have to worry about the wax seal leaking.
Doesn't feel like camping to me. YMMV.
"It's not what you know that's important...it's what you do with what you know." -H.G. Rickover