Welcome to the forums and that's a nice MH. If I lived near you in TX I'd say replace all 6 so I could buy them and use them on one of my trucks. Unfortunately a 275/70 is not a normal truck tire size so selling them for $200+ each is not likely. Since you know the history and stored inside with some weight off the tires I'd replace the front two tires with Toyo or Hankook. Here's
61 posts on Goodyear and rivering. As you found out, truck tire places say they are fine while most on here will say replace all of them. I would carry one of the replaced front tires unmounted on the roof wrapped in alum foil and plastic wrap as I actually had a truck tire place laugh at me when I needed a 275/70. Here is a previous post on carry spare on the
roof.We are into weighing our MHs when loaded up and adjusting the tire pressures for the weight. My educated guess is you will need 105 in the fronts and 95 in the rear tires. While 5100 miles is not enough to tell about the alignment by looking at the front tires, you can check the toe in by measuring between the two same spots on the inside of the tires (front/back) and you want 1/8" toe in.