Moved thread from the General Tech and Repair section to the Sierra sub-forum since the OP is asking where the furnace access panel is, in his Sierra trailer, which is model-specific information.
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Dan-Retired California Firefighter/EMT
and Zoe the Wonder Dog(R.I.P.)
2016 PrimeTime TracerAIR 255, pushing a 2014 Ford F150 SCREW XTR 4x4 3.5 Ecoboost w/Max Tow Package
4pt Equal-i-zer WDH and 1828lbs of payload capacity