If ST trailer tires, internal heat buildup will kill them - from being under-inflated, overloaded and/or towed over speed rating. Internal damage is cumulative too. If they've not been treated correctly for some time or history is unknown, I'd replace them pdq.
Tires do heat up though from travelling down the road and the pressure will go up which is perfectly normal. Without an IR gun, you're guessing as to them being too hot. Tires on one side of a trailer can get much hotter too if one side is out of direct sunlight. Have you set the pressure "cold" before heading out on the road? 30 psi is waay too low if LRC ST tires and asking for a tire failure.
You might take a read through the RVtiresafety.net blog and post on tire temp.
here and his posts on ST tire pressure.