There might be one ST tire made here in the USA but most are produced by Asian companies. Maxxis is a good ST tire for rigs up to 10K or so pounds as I have had reliable service on our 10K# 32' TT for the past 4 years, heavier rigs such as your Everest will get better service out of a set of LT Michelin X-ribs our similar type tire.
Most RV manufacturers put barely enough axle and tire to begin with on their rigs, and they are more concerned with price point than quality when it comes to the tire they choose to install.
Our current 7 year old rig has only had ST tires on it with the stock tires lasting nearly three years before changing them out to a set of Maxxis ST tires. Nearly 50K miles across both sets and not a single blowout or even a slow leak, this includes many miles at interstate speeds that out west exceed 65mph.
Your heavy 5er requires tires that can handle the GVWR of your rig and then some, It's all about safety margin and the bigger the cushion the better. One of the reasons our ST tires have performed well is that they are rated to carry the entire GVWR of our rig and then some, plus making sure they were aired to max pressure as stated on the sidewall as ST tires can overheat and fail when tire is under-inflated.