The 25'6" length is tip of tongue to the back of the bumper, or maybe spare tire, if equipped. The 21QB replaces our 19RD, which measures 19'7" on the body only. Yours is probably 2' longer on the body length, but not positive. I would wait and measure your TT before ordering a cover, unless a member with a 21QB chimes in with the exact length.
2012 Jay Flight 19RD
2016 Ford F150 XLT 2X4 SC 3.5L Eco Max Tow
2010 Tundra TRD DBL Cab (Traded)
1 Spoiled Dog