If you can't find the water heater, you really need to take that RV bootcamp mentioned in post #3 above. Towing and operating an RV involves risk to yourself and others. If you can't take a weekend class, find an RV mentor in your area, or ask on this forum if there are any Hi-Lo owners in your area. RV'ers are a friendly lot and you'll find help.
On to your question. There are usually 3 propane-powered devices in an RV. 1. The stove/oven combo. You know where this one is. The other 2 are: 1. The RV 'space' heater that heats the interior of the RV. The 2nd is the water heater. Both of these two will generally be located on the floor level of the RV. With the top of your Hi-Lo in the up position, walk around the RV and look for 2 slotted or vented panels on the bottom of the exterior walls. (There will usually be a 3rd cover behind your refrigerator, but you know that one). When you locate those covers, open them up and see what you see. You should be able to figure out which is covering the space heater and which is covering the water heater by looking inside those corresponding spots to see what's inside. On my RV, the by-pass valves on the water heater are not accessed through the vented exterior door, but from another door on the side of the water heater.
Good luck