There is always the possibility of local heating from a section of heat tape. If the PEX is Pex-Al-Pex the heat distribution through the aluminum barrier might help. Another method would be to run the pex through electrical conduit wrapped with heat tape and insulated.
As this post might be from Alaska, there might be a need to do this. Otherwise, pulling pex through aluminum conduit placed under the insulation in the attic should be sufficient without the heat tape, and the conduit will give some protection from accidental damage.
The pipe should be under at least six inches of fiberglass batt, never exposed.