It's a little hard to read but I'm wondering if it's the 2nd 20amp from the top. All I can suggest is pull a few 12v fuses, maybe starting with the 20amp mentioned and see if the furnace is turned off.
As a second thought, could you configure a 'cover" for this switch that would not be in your way and yet allow for protection against accidentally flipping it?
Or, change the switch to a type that is less prone to being accidentally tripped?
Days camping (2016)----181 days
Days camping (2017) --- 21 days
2016 Wildcat MAXX 28RKX (33' TT), 2007 13' Scamp
2015 Ram Laramie Hemi, w/air suspension
30 years RV'ing
12 different RV's