Maybe use 3M-80 or 3M-90 spray adhesive. Do a search - either of those would likely work well. When I removed mine to install the Dynamat sound deadening, it looks like Ford used 3M-80 or similar. It was just attached in spots, and came off fairly easily without destroying it.
I applied the adhesive-backed Dynamat, then re-used the factory foil-backed heat insulation. It REALLY helped deaden the noise.
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