Hi CeeCee,
The brochure should be close, but consider that you may not have the rig perfectly level when towing. Ours is tallest at the front A/C unit and the unit tows very slightly nose high (< 1").
The best way to be sure is to get on the roof with a measuring tape while sitting on level ground, hooked up to the tow vehicle. If you put a board across the A/C unit, with some help on the ground, you can get an accurate measurement as you'll actually be towing.
Our Landmark is spec'd at 12'11" but I measure it at 13'1". I then set the GPS for 13'3" to allow for resurfaced pavement at low overheads. There's one in Dalhart, TX that's 13'7" and even though I know I've got 6 inches to spare, every time I go through there I wonder how they do the resurfacing.