Jerry,
Welcome to the Heartland Forum and I hope you have many great trips and experiences in your Landmark.
Heartland RV's has a hitch with 1 1/2" receiver that you can mount on the rear of your Landmark it is only designed to mount a bicycle rack and carry bicycles. It is not designed to tow another vehicle or trailer. If you tow a vehicle or trailer it will void the frame warranty (as per Heartland and Lippert). Also if you did tow a trailer behind the Landmark, it will probably will exceed the maximum length allowed in your state or another state, which is usually 65' or 70'. Your total length of your truck and trailer is between 53' and 59' without an additional trailer. Also some states do not allow towing two trailers with one tow vehicle. Do research on the internet to determine the regulations in your state or the states you plan to tow. This will save you money and keep you from having problems.
Happy Trails to you,