Fixing some rotten wood, what type of wood should I use ?

I ditto the advise that rot-resistant wood like cedar and redwood don't have mechanical strength.
I use fir for my camper rebuild, but I go to HD and select several boards to find one with no knots and high density.
Let it dry for at least couple of weeks what will also expose internal tension that curves the wood when drying.
Seeing what manufacturers used on TC, I think they get wood from pallets recycling.