I am in the process of building a cabinet incubator and will be using Mahogany ? I think if the wood of choice is not so important as to how you preserve it ..eg varnish etc .For myself I will be lining the interior with what we call "" puck "" board , a sort of plastic Plexiglas that is used to line poultry barns etc and helps with the disinfecting part of cleaning a barn .By lining the interior you keep in the moisture as well as making a clean up a breeze and protecting the wood as well ( as long as you seal it properly ) Cedar is a very light wood and also will absorb moisture ......but is almost rot proof which might be a benefit ?? Also cedar will seal quite well with a oil on the outside .Personal choice would be my answer .