Went Lengthwise in our 28 ft'er...it was a real PITA to cut and fit all those edges! I don't think I got to use more than about 10 full 'boards' out of the 5 boxes!
I used Prego 'Indian Tigerwood'. I never could get the hang of inserting the boards as shown in their instructions...I ended up engaging the tab lengthwise, then carefully tapping the board back into the previous board's groove with one of those plastic tools against the other end of the board...worked much better!
Ray & Pat; Morada, CA