The bed and cab are going to flex too much for you to use a solid system like that; even just going down a bumpy road you can watch the flex in the side view mirrors. You could always separate it into two pieces with bracket on the ends so you could drop a filler piece in. Also you're going to get enough air moving between the cab and bed that a solid surface is going to make a ton of noise. If you have a sliding rear window open it while driving down the road and you'll see how much air and road noise there is between the two. As noted, your wind deflector probably isn't doing a ton to help either.
05 Tacoma TRD, SR5, V6, etc
1978 VW Westfalia
2007 Suzuki DRZ400s
Who is the happier man, he who has braved the storm of life and lived or he who has stayed securely on shore and merely existed?
Hunter S Thompson