I’m not too experienced with B-118 - MM-111 is the go-to rootstock in my climate - but I seem to recall reading that it doesn’t like damp soil. It’s possible that it does require staking, at least for a time, to keep it upright under your conditions.
You might consider P-18 as an alternative - Cummins describes it thus: “A Malling 4 x Common Antonovka hybrid from the great Polish rootstock breeding program at Skierniewice. (No, the “P” doesn’t stand for “Polish” or “Poland”, but for the Polish word for rootstock.) Slightly more vigorous than Budagovsky 118, about 95% of standard. Extremely winter-hardy, as well as tolerant of “wet feet”. Resistant to collar rot, scab, mildew, and gall; intermediate tolerance to fireblight. No burrknot tendencies!”
Of course, if the soil is damp enough, P-18 might require staking for a time to prevent leaning, too.