We also have as 2017 E19. I pulled the furnace vent and furnace last summer under the expectation I would be able to install an access panel to service the control board and sail switch. I was encouraged by posts like (see ~8:40):
Apparently, the furnace installed in our 2017 E19 is of the vintage different from Ed's 2018 since the sail switch is installed behand a panel near the bottom of the furnace rear. Long story is that I cannot access the sail switch without removing the furnace from the trailer. Err. You may want to pull your furnace to see if your 2017 is different than ours and more like Ed's 2018.
edit - see my earlier post on this topic:
https://www.escapeforum.org/forums/f...tch-21484.html