Most (but not all) boas will climb if given the chance: though my biggest male had a ledge in his viv and he never used it. If you want to add something to climb on for it I'd go for it. I'd add hides in there too just to give it extra security: some of my baby boas used their hides and some didn't but I liked to give them the option.
For boas not doing well in tubs I've started all of mine in them and have/had no issues.