The only way i found really working out for me is to have a tank pull aggro w/ hate and a few hits before launching the seals. I hardly ever get hit when the tank is a few lvls higher than I am; otherwise, i switch to heavy armor and/or activate soul gard.
The seals getting us aggro'ed is a reality whit which we have to compose. Learn to use it as a way to pull mobs and it can become an advantage of the class instead of just being a pain in the butt:)
Mobs are going to turn on you when you seal them up. We have a tool to combat that (Soul Guard), just flip it on before you seal up the mobs and then wait for the mobs to turn to your main DD. Drain a few times if necessary to fill the hp, then melee away to get a little of that MP back =) Rinse repeat.
Soul Guard is your friend. If you need to Dreaming spirit due to incurring high damage with Soul Guard on (the chain-draining mobs in Pagans for example), by all means utilize it. We have plenty of tools to be arguably the best crowd controller in the game vs mobs. Soul Guard on, Despair, Blockade, Winter, Binding, Silence, Dreaming spirit as required, and Drain up to full hps as required.
If you toggle Soul Guard before you try any sealing shenannigans you should do just fine, until Hellbound where our seals (lowbie ones anyway) don't function with any level of reliability unless heavily overenchanted.