My Roadtrek has a tag - from Roadtrek and not Chevy that says, 80 psi rear and 50 psi front. When I first got the van I spoke to Roadtrek about the front number and was told that for the front tires - and only the front tires - 50 was the starting point (and what Chevy recommended before the conversion). I was told to increase the front tires by 5 psi, test drive and see if I liked the handling better - and do this up to and no more than 65 psi. I like the handling best at 60 and that is where I leave it. The rear tires need to be at 80 for the added weight of the conversion and I was told not to change that higher or lower.
For the OP - you might try calling Great Western and discussing this with them as they know their Class B best.