The tanks should be held to the underside of the trailer in a sheetmetal pan. Looking from underneath you will see a steel box, 1 to 2 inches deep hanging off the frame rails. This is attached to the frame with bolts. This pan will drop out of the trailer and the tank(s) should be lying on the floor of the pan, on top of a styrofoam wedge that holds the tank in position. This should be under the bathroom area, if you ar working above the axles you are dropping the fresh water tank. :eek
I would reccomend that you have a couple of floor jacks under the pan as you pull it. You also need to pull the inspection plates before dropping it and detach the dump handle(s) as well as the outlet from the tank.
Two other things, you will get more responses to your questions if you fill out your profile more completely, and the model of your trailer would help too. I do not know of a Land Crusier model. Most are called Land Yachts, but there is also other identifers such as Tradewind, Globetrotter, Sovereign