Correct tire pressure on 5th wheel?

ST tires should be set to max as indicated on the sidewall which is what is displayed on your rig's sticker. LT tires can be inflated to the weight they are carrying, not so with ST tires as anything much lower than max psi will cause them to overheat and eventually lead to catastrophic failure.

Roman Duck wrote:
Air pressure is determined by your gross axle weight. Once you know how much the camper weight(axle/tire weight) is, you can inflate the tires to the correct pressure.
You can find a inflation table showing the correct weight to air pressure ratio at the tire manufactures web site.
Over inflation or under inflation can cause tire overheating, which will lead to blow outs and shorter tread life. Get it right if you care about your your camper, as many have been lost due to tire inflation issues.
As far as getting the right weight take it to a public scale, even better if you can weight each tire separately.

+1

Read what it says on the side of the tire. There is no such thing as a reputable dealer. It could be you have D load range tires and 45 psi would be the max for that tire.
Personal story. I had a 5er that used E range tires. Went to one of the largest tire dealers in the area for 4 new tires. He didn't have 4 of the kind of E range I wanted so they had to order them. The next day I took in just the old tires/rims. I picked them up later in the day, went home, and started putting them back on my 5er. As I put the first on one I checked the air pressure and it was at 45 psi. It was then I noticed it was a D range tire. I called the tire dealer and he said he put D range on them because he couldn't get E range tires. I had ordered E range, paid for E range, and needed E range for a 5er my size. When I took the rims/tires back the owner I got on them about why D range tires and not telling me. The owner would only reply "We couldn't get E range tires." When I asked about paying for more expensive tires but them installing a cheaper tire he finally replied "We didn't think you would notice." Reputable? The Attorney General's office didn't think so either.

Air pressure is determined by your gross axle weight. Once you know how much the camper weight(axle/tire weight) is, you can inflate the tires to the correct pressure.
You can find a inflation table showing the correct weight to air pressure ratio at the tire manufactures web site.
Over inflation or under inflation can cause tire overheating, which will lead to blow outs and shorter tread life. Get it right if you care about your your camper, as many have been lost due to tire inflation issues.
As far as getting the right weight take it to a public scale, even better if you can weight each tire separately.

"However, the faded sticker on the side of the trailer and the sidewall of the tires both say weight limits based on 65 PSI."

There you go.....65PSI is what your faded sticker and the sidewall of tire states for max load which is what you want to run your trailer tires at.
Check/adjust tire pressure 'COLD' (early am prior to being run on)

CMunrock wrote:
These are new tires installed by a reputable RV dealer, (about 5 weeks ago), so I assume they meant to inflate them to those pressures.

Don't assume that this reputable RV dealer" inflated them correctly.
I seriously doubt that 45psi is the correct pressure.

Look on the tire sidewall and inflate them to the max pressure that is indicated there.

Go with what the tire says. If it says 65 than put that into it.

What do the tires say?

I would bet that 45 is too low though. Mine are supposed to be 80

What does it say on the tires? I had new G614's put on last fall and the installer only aired them up to 85psi not the 110psi called for by the placard. Which I soon remedied.