Mike , assuming you still have the old units .
Go flip one over and you will see the little pans .
If they are ok just take them off go up on the roof and install
on the new A/Cs .
However it wont hurt a thing to leave as is and install later
the water will just run on the roof . .
The water drips into those pans then a hose goes inside the coach
there it ties into your drain system .
You are supposed to use 2 gaskets and cut a notch between
the 2 for that hose to pass through going inside , caulk it good .
The idea is the pans catch the water , carry it back inside then down
the drain hoses .
However if the drains get stopped up then the pans just overflow out
onto the roof instead of in the floor .
Pretty neat .