Our Sunseeker often has pressure near 150 psig and I have had no problems. When the water system is closed and the water heats up, the water expands and the water heater relief valve drips. Pressure relief valves are rated to open at the set pressure but will normally begin to leak at about 95% of the rated set point.
One problem that I have is that I can't open the toilet valve when the system is under high pressure. I have to first crack the sink faucet to relieve the pressure.
Once I could not remove the water filter canister while dewinterizing the coach. I had flushed and filled it the previous day. I don't remember why I didn't install the filter then, but I forgot that the water heater was turned on and when I tried to take the water filter canister off it had built up so much pressure that I couldn't turn the canister.
I try to keep an air pocket in the water heater that's supposed to allow enough expansion, but it seems to fairly quickly go away.