Burn tons of redwood in my California fireplace ;)
Redwood will dryrot, but it will take longer.
When average fir used on fence post will rotten in 2-3 years, redwood will last 10 or even longer if kept dry.
But redwood has very poor mechanical strength, so would be one of the last recommended for TC
When I was rebuilding my TC, I spend lot of time scratching my head in "what was those builders thinking" mode.
Unbelievable how cheap some of those builds are, so lot of time I added on improving the build.
Older campers had fiberglass insulation, what has pretty symbolic performance. Replacing it with Styrofoam, or better urethane foam will be big improvement.