Which tow vehicle tires?

I have a 2010 F-150 Super Crew long bed ( 21,000 miles ) that I bought new from my local dealer. This pickup came equipped with a set of Michelin LTX A/T2 P265/70R17 tires that developed small fine cracks on the sidewalls. I don't use petroleum based tire treatments, but wash the tires occasionally with mild soap and water and keep them covered with the same type of white tire covers I use for my travel trailer. I recently took my truck to Ford Quick Lane and I asked the manager to inspect my tires for safety. He explained that the cracks are "normal for Michelins". I seriously doubt that his statement was true and I am planning on replacing them. I am not sure if Michelin will make them good, but I haven't tried yet. I tow a FunFinder 189FBS travel trailer that weighs 4,000 lbs fully loaded and I am not too comfortable towing with P tires. I am looking for a US made all season LT tire that is smooth riding but appropriate for towing a trailer like mine. Any ideas?

Thank you,

Mike