Travel/Lodging for Commercial Requirement Subject to the JTR/FTR?

If we have a commercial requirement that includes travel/lodging and is anticipated to be entirely FFP and not on GSA schedule, do we have to require the contractors to propose that travel/lodging in accordance with the JTR/FTR? I have a branch chief that's tell me that all travel/lodging must always be at or below the GSA per diem rates in accordance with the JTR (pretty sure it's the FTR that applies since it's CONUS but whatever) due to FAR 31.205-46 but I thought this only applied to cost contracts, not FFP.