TruOil is not waterproof.A good finish like polyethylene is. But doing the barrel channel is a good idea. Checkering should be done too .You can thin the finish a bit with solvent and apply with a toothbrush. You could then wax it if you like.
A good case , you can get waterproof ones , is ok as long as you understand that you should never leave the gun in the case when you get back to camp.
At camp ,keep the case open ,clean ,dry the gun and coat with a good rust proofing like the one I use , RIG preservative grease. In the field you can put some tape OVER the end of the barrel but NOTHING IN the barrel. You can shoot right through the tape without problems.
If you have clear covers on the scope take the covers OFF when shooting as they distort the picture !
And Watson , bring your revolver !