Family looking for 1st Trawler

I'm not sure the OP is interested in this somewhat philosophical debate, considering also, as I understand, that he's seeing the circumnavigation as a one-off project, rather than a radical change for a liveaboard lifestyle with a very long term horizon.
And as we know, boats capable to go RTW can be - and actually have been - built with just about every material: not only plastic/steel/alu, but even wood. Which btw, for living aboard, is hands down the best alternative, way above anything else.

That said, the only boats I ever came across designed to withstand a catastrophic engine room fire were built in steel.
It isn't just a matter of material of course, and the vessel must be designed from the ground up with that event in mind (fully water & fire proof bulkheads+doors, get home engine in a separate compartment with its own fuel feed, structural tanks, and so forth).
But for any builder who wants to design a boat capable to survive such event, the choice of steel is a no brainer, really.
Not only glass and wood (obviously), but even aluminum ain't as good as steel, in this respect.