MRD tanking at low levels is much easier than GLA tanking. Really, your best bets are to either mark your targets and make light use of flash (While using your fast -> Savage combo), or just flash spam and rebuild your MP with riot blade and then repeat. That's what I do, anyhow. You're not doing anything wrong, it's just that SE really screwed over GLA/PLDs with enmity generation before level 40.