This is, as Faldo the catowner pointed out, one of those situations where the past tense of a weak verb looks wrong but isn't. Personally, I would take the trouble to break it out into a form which didn't put me in the position of having to make a choice by adjectivising the verb - "I went scuba diving". A kind of imperfect perfect tense, if you will. Well, better than the alternative tenses anyway. "I scuba dived" or "I scuba dove" just sounds (and feels) awkward.