Wish me luck on the pics.

They are still there, now for you to find them.  Am not sure if you have a 2 valve or 3 valve system but there are normally 2 ways to access them.  The first is by opening the storage area door (toward the rear of your 171) and then removing the panel that is located to the left just inside the storage area and reaching inside.  Unless you are a great contortionist, this way doesn't work, and beside you are going to have to do it all by feel - not good, considering the consequences of if you don't turn the valves all the way to 'open' or 'closed.'

The better, and more difficult way (but you only have to do this the first time) is to remove your mattress and unscrew the luan board underneath and lift the whole board up so you can locate the valves - they will be directly behind the HW tank.  Turn both or all three opposite to how you found them - make a note so that the following spring you will not have to guess as to what to do.  Before putting the luan sheet back down cut an opening directly above the valve location, the opening I cut was 5" x 7", enough so I can shine a flashlight in the opening and get my hand in at the same time.  The next time you winterize or un-winterize the system you will only have to lift up a corner of the mattress and with flashlight in hand, turn the valves.  On my 177, it takes roughly a minute for me to lift up the mattress and turn the 3 valves and then drop the mattress back down. 

Has FR finally designed the 'free lunch', or maybe the cut off valves were left off by the factory and we got thru last year's mild winter very fortunately, or ...?