Leaking out into the cabinet?
Do you mean inside the camper
OR
Into the outside compartment?
Inside the camper:
Hot line fitting at top or cold line fitting out bottom (only 2 areas where it can leak from)
Outside compartment:
Pressure Relief Valve (can weep when water it heated)
Drain plug (new nylon plug and clean up threads would probably fix leak)
Gas Valve thermocouple gasket (gas valve screws into tank)
Other than a 'crack' in tank those are the places water could leak from on tank.
Might have been easier to locate/ID leak with WH still installed by cycling it thru a few heat cycles and using paper towels under things to find source of leak.
Now that it is out.......
Need to get a plug to screw on hot out and an adapter to screw on cold in so you can hook up a garden hose to cold inlet.
Should be able to find fittings at ACE Hardware
Then hook up garden hose...fill tank (Open PRV with lever to expel air/fill tank) then try to ID leak.
Course leak may only occur when water is heated OR it may have been loose hot/cold fitting
Where did you find evidence of leak.....inside camper/outside compartment?