I would check with a dealer who sells Samson tires to see if they have an inflation pressure chart. Keep in mind the pressure sticker on the motorhome applied to the tires that were on it from the factory. Over the years tire construction and pressure ratings change. I'm relatively sure it didn't come from Ford with Samson tires. What was true in 2007 for a particular brand and model of tires that were originally installed on the motorhome may not be relavent for the tires you currently have on it.
Our 2001 F53 chassis came with Goodyear G670 tires size 245/70R19.5 load range F. The recommended tire pressure was 70 psi. A few months after we got our motorhome Goodyear sent out a bulletin raising the minimum pressure to 75 psi. In 2006 they chnged the tire construction and raised the pressure recommendations to a minimum of 80 psi.
If we had used the sticker on the door to determine tire pressure it would have been a minimum of 10 psi below the recommendation for current tires.