First thing that occurs to me is to wonder how fast that puppy will fill up. I've been involved in some sewer planning projects, and average water use in a residential setting is assumed to be 125 gallons per person per day! Most of which goes down the drain, of course.
I s'pose RV use might be a little lower than that, depending on appliances etc, but still- at $20.00 a pump it won't take long to make your sticks-n-bricks sewer bill look like chump change.
" Not every mind that wanders is lost. " With apologies to J.R.R. Tolkien