Two Seat Cobra Trailer Tire Replacement

On our single axle two place glider trailer I destroyed the two original tires that were on it when I acquired it. One was just a cut in the sidewall that I discovered while parked. The other was a total failure while on the highway; and I wasn't aware of it but for another driver alerting me. The tire was completely missing and the rim was destroyed; this while towing behind a 21' class C. The replacement wheel and tire were from W&W. Though it does seem to tow somewhat better with the newer tires, I have never been happy with the way this trailer tows and I am seriously considering adding a second axle. The Airforce Duo Discus trailers are duel axle.