DO NOT caulk the A/C unit. First thing to do is to tighten the four bolts inside and see if it is just a little loose. If this does not stop the leak, you will have to remove the A/C unit and replace the gasket.
The gaskets are available from any RV dealer and takes about 30 minutes to replace. The prime thing is to not over tighten the gasket.
But DO NOT caulk the A/C unit gasket.
Other leaks you can use the Dicor sealant or Eternabond tape.
Amateur Radio Operator (KE5DFR)|Full-Time! - 2012 6.7L Ford Crew Cab Dually -2013 HitchHiker Champagne 38RLRSB - Travel with one Standard Schnauzer and one small Timneh African Gray Parrot