I see by the spec's on your trailer web site that you have 205/75/14 tires. A few years ago it would be a no brainer.....just buy Goodyear Marathon's! Now they are made in China, I have 3 on my Pontoon boat trailer with about 2500 miles and so far so good, as it should be.
If I would have known about the "China Syndrome" AND known about "Denman" tires I would have bought the Denman Express S/T radial. They are still made in the U.S.A. and you can see them at
www.Denmantire.com ...look at "catalog", the Denman Express S/T is in the lower right hand corner of that page.
Yes you can upgrade to a radial and yes you can go from the 205/75/14 which is rated at 1760 lbs. and is 26.1" The 215/75/14 is rated at 1870 lbs. and is 26.8", the fitment shouldn't be a problem, hope this helps......Dave