For the pressure the type of tire is important and the maximum load.
But also the weight on the seperate tires.
Mostly the GVWR ( Gross Vehicle Weight Rating) is used for that , but better would be weighing when loaded, and even better per tire.
If you have all that you can put the data in my Traveltrailer-tire-pressure calculator wich can be found in this map on my public map of skydrive.
But if you give the data needed , I wil do it for you and give a picture in the answering post.
My advices given with the spreadsheets is mostly higher then you have on the sticker, because I add a reserveload and use a better formula wich leads to the same deflection of the tire over the whole range of pressure/loadcapacity.
But standard advices more often given of maximum of tire , I dont give, and then my advice can be lower.