Mine is a 25RL which I presume means and I have measured inside front wall to the back inside wall is 25 foot while the RL means rear living. I have measured out side length and it come to 27ft 8inches.
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2001 Ford F-350 DRW 7.3
2011 25 RL Wildcat
former fiver 1976 Fourwinds had for 35 years
FWIW, when we had a pop-up we always described the length by the box size. 10', 12', etc... I honestly never bothered to measure it with the beds extended out.