I have been thinking about this.. Since this is a LONG TERM parking spot.. I think I'd have a contractor drop in a proper septic tank and drain field.. Make sure it can take 100 Gallon "Hits" (dumps from the RV) from time to time.
My RV has 3 36 gallon tanks. one can be ground dumped and I do from time to time (This one services only a shower and wash basin, not the kitchen sink) the other two always go into a proper dump (hole in the ground sewer system).
When Wife was around we dumped 2x/week. by my self 1/2x per week .