Mine is on the front, street-side corner of the trailer. It is behind an exterior vented panel that you open to gain access to the heater and the water tank drain. It is close to the fill point for the fresh water tank and the city water inlet. Yours should be located similarly.
Go on the outside of the HiLo. Find the drop down water heater door. Then you will know wqhere to look inside. Both of the HiLos I owned had the water heater on the drivers side close to the front.