Keeping the Bonemass power at the ready is essential in Mistlands until you have become accustomed to things and access to equipment that is effective against seekers. If I have the power off cooldown and there's more than one enemy along high rank seeker, I won't hesitate to pop it as soon as I can.

High rank soldiers should be ignored and escaped from under any circumstances if you are playing solo, there's just no value in fighting them unless they are blocking you somehow.

Root harnesk can be very helpful as well. If you're using padded armor with root harnesk, it will greatly mitigate any piercing damage, which is the primary damage type dealt by seekers, but even that shouldn't be relied upon too much. You'll have to try how it works first hand with your preferred combination of food and equipment.