op wrote:
Was this guy blowing smoke or does he have a point?
He was correct.
Bias ply tires run hot...hotter than a radial especially those tiny 12" tires and especially at highway speeds.
Years back 12" tires were common on small trailers ...rv and non rv and were very problematic.
One of the first mods I did to any trailer (rv and non rv) with a bias ply tire was dump them and go with a 13" or 14" wheels and P radial tires. That move eliminated bias ply blues issues as we called them back then.
etrailer can help you with axle/hub upgrades. Give them a 1-800 and tell them what you want and what you have. Those folks have been around for a long time and are well up on those type mods.