a quick search showed these on Ebay. There may be an issue with these as even though they are advertised as 12x1.5, 14x1.5 is mentioned in the specifications.
I'd contact the seller for clarification...
you could try a bead of silicone caulk. try one bead on the underside of the carpet for a trial. let it cure completely before putting it back in the Bronco.
I've done that on carpet runners at home, keeps them from slipping around but they peel right up for repositioning.
are you saying the Bronc doesn't throw warm air?
there is a possibility that the thermostat isn't working properly or the grill shutters are staying open.
perhaps a trip to the dealer is in order if it isn't throwing heat.