Welcome to the forum
I have done slide floor replacements but not a roof. Thinking out loud:
Maybe you can “hyper extend” the room so that the sidewalls are exposed giving you access to the fasteners. To hyperextend the room you remove the facias and then it depends on type of slide mechanism. If it’s cable or Schwintek this procedure won’t work and you’ll have to remove the room.
What type of mechanism does your have?
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2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.