I can only help from what I have, a 99 Adventurer 34V. I have 2 thermostats, both are Coleman. The main thermostat is located on what I call the hall wall between the main living space and the bedroom. It's on the bathroom side near the forward corner. The main thermostat is a dual thermostat in that it controls both the heat and air and it indicates such,and it does have an "OFF" position and thermostatic slide setting. The second thermostat is located in the forward bedroom wall, right side. This thermostat is only controls the overhead AC unit in the bedroom. Both thermostats are Light tan or neutral colored. The main thermostat at has a selector for HEAT or COOL. To make the furnace operate place in the HEAT position and set the temperature slide above ambient room temperature. You will hear the furnace blower cut on immediately, it's purging the burner chamber, within a minute or so you will hear the furnace make a rumbling sound when the burner ignites, and you should have instant heat at the floor registers. Make sure ALL of your floor registers are fully open and unobstructed, and the Intake Air which is normally in the bathroom is clear and open. Most likely if your furnace came on in your absence it was because it was set to heat and the temp set was above ambient temp. and the LP shut off valve was open. The Main shut off valve is in line and just aft of your supply tank which is located in the forward basement compartment right behind and below the driver's seat.( The most forward compartment on the left side). Some units may have a shutoff valve at or near the furnace which is located in the rear left side of the coach. You can locate the furnace by it's tell tail dual over and under intake and exhaust ports on the exterior of the coach.
If you haven't found one yet I can e-mail you a copy of Winnebago's Instructions for Furnace heat. One last caution, make sure your CO2 and Smoke alarms are functional. It's unnerving to know that your literally sleeping on top of the furnace. I also keep the bedroom windows open just a Tad. An annual inspection and operational check is a highly recommended. Sounds like you've already completed the operational check.
Also I need to mention if you slide your thermostat below cabin temperature or select OFF on your heat while it's running, there will be a delay before the furnace shuts down. The furnace is designed as a safety measure to cool the burner chamber prior to total shutdown.
Also most likely your roof AC was not working because you had heat selected on your thermostat