Correct me if I'm wrong, but that's a name that was originally used by one company (The Tonneau company) for some cheesy, vinyl peace of garbage, that turns your bed into a swimming pool every time it rains.
Of course if that's the kind of bedcover you have..... Especially if it was actually made by the Tonneau company (do they still even make bedcovers ?) then I guess it might work for you.
But the thing is, their are actually guys who call "real bedcovers" a Tonneau ! WTF ?
Personally, I own, and love, my "fiberglass bedcover" (or just 'bedcover' for short) made by Snugtop
'Tonneau' covers are for sissies

LOL
Fish
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2008 F150 5.4L XLT Supercab, Magnaflow true dual exhaust, Pro Comp 7089 wheels,
Bilstein 5100 shocks with 2" front lift, BFG AT 285/70-17"s, Snug Top SL PTM bedcover,
Roush grille, Hella blackout headlights, Westin step bars, Powder coat bumpers,
4% rear 3 window tint, 15% front sides