jharvey1025, you mentioned the light rail, which is not the same thing as the PATH train people are talking about. There is a light rail stop very near the RV park, but it goes just a couple of stops to a station where you pick up the PATH train to NYC.
What most people do is walk a little farther north to the PATH station, bypassing light rail entirely. (And FWIW, the light rail doesn't use the NYC metrocard at all.)
Assuming you're willing to walk to the PATH station and are indeed talking about a combination of PATH trains and NYC buses/subways, you didn't say what your objection was to buying separate cards. If it's keeping track of two cards, then Lumpty's point is valid--the metrocard can cover both the PATH and NYC bus/subway systems.
However, if your objection has to do with not being able to use an unlimited-ride metrocard on the PATH train, you can't get around that. The metrocard works on PATH trains only if it has a balance that will cover the pay-per-ride fare on the PATH train.
You can use one metrocard for both if:
(1) you put a balance on it and use it to pay-per-ride on both the PATH trains and the NYC system, or
(2) you buy an unlimited NYC system pass and add a balance to it to cover the PATH trains.
You CANNOT buy an unlimited multi-day metrocard and expect it to work on the PATH trains.