A line of foam insulation (about a quarter inch thick) is applied at the bulkhead. There is a rubber seal in the cover at the tailgate. Proper adjustment of the latches should pull it down pretty good.
Current price on Worksport.com have the cover at $845.99.
Just received Worksport AL3 Pro cover for my TRD Sport. Well made, easy install and a great price.
Initially noted that these would not ship until after June 1, but received shipping notice on 5/29 and was delivered 5/31. Great addition to my truck.