Map the interfaces before choosing

Record truck bed width, rail shape, cab and rear-window clearance, rack position, tonneau operation, tailgate path, toolbox lid swing, and the tools’ weight. Then compare the mounting instructions for each setup.

Constraint Headache-rack toolbox Bed-mounted toolbox
Bed floor May preserve some floor space Occupies a bed section.
Rear access Can affect rack and window access Can affect bed-side or cover access.
Tonneau Needs rack/cover compatibility Needs cover and lid clearance.
Mounting Rack and toolbox interfaces both matter Bed rail and toolbox hardware matter.

Google/Bing query evidence is sparse, so this is a fit map rather than a product winner.

Limits

No truck, rack, toolbox, cover, or load was tested. Exact fit, safety, and payload remain model-specific.