I found the Pelican case I intend to use for this project. I recall buying it on Amazon because it was dirt cheap, but I had no immediate use for it and it ended up on a basement shelf. I'm mostly using the Pelican because I already own one, but it has a lot going for it. Crushproof, waterproof, and just the right size to hold both the electronics and the RTD itself, which is about the size of a C-cell battery. I also like how it has a robust carrying handle. Despite the fact that it's likely waterproof, the Smoker Controller doesn't live outside! It will need to be carried to and from the house.
My first thought for mounting the hardware inside is to not mount it at all. I'm thinking a 1/8" plywood box that fits snugly inside, secured only with foam tape. Everything gets mounted to the box so I don't have to pierce the Pelican's exterior to screw things into place. A primary concern would be ensuring the wooden box doesn't interfere with the waterproof rubber gasket or prevent the lid from closing.
The RTD also has a longish twisted-trio leadwire (maybe a meter?) that would have to be coiled up and stored inside the Pelican case as well. I had an idea for a laser-cut spool that accommodates the RTD's wire, mounted on a 1/8" plywood board that would be foam-taped to the inside of the lid.