An exemplary embodiment of a heater assembly includes a heater housing structure defining an elongated heater chamber having a first port and a second port and defining a wetted side on the interior of the heater chamber and a non-wetted side on the exterior of the heater chamber. A resistive heater element is has an active region disposed within the heater chamber, free of any brazed or welded bulkhead members. The housing structure includes a first heater terminal opening and a second heater terminal opening, a first terminal end of the heater element passed through the first terminal opening from the wetted side to the non-wetted side, and a second terminal end of the heater element passed through the second terminal opening from the wetted side to the non-wetted side. First and second seal members are disposed on the non-wetted side respectively onto the first terminal end and the second terminal end and in contact with respective first and second seal surfaces defined on the housing structure. First and second fastener members respectively engage the first terminal end and the second terminal end and the first and second seal members. The housing structure may be fabricated of plastic, with respective current collectors in the form of unitary wire forms disposed at opposite ends of the housing structure.