I don't want to come across as one of those self-righteous types, but in my opinion a 50-gallon plastic tub would be cramped for anything except a hatchling or juvenile russian. For an adult russian I think it would lead to a poor quality of life.

A redfoot can get 1.5-2 times as long as a russian, so a 50 gallon tub would be even worse.

Also, you really don't need to hibernate a russian. If you want a tortoise, consider a russian for ease of care and just give it about 8 sq ft of space to live in. Of course, more is better.