How do yall keep your trailer tires from rotting when they're sitting in one place out in the sun? We had 3 blown tires on our last trip with this trailer. Just got some new goodyears on it and want to make them last. This is a 18' HD carhauler that sits as long as 4 months at a time before it is used, but when it's used, it's nearly maxed to capacity. Suggestions?