Trailer tire question

[Darrell]

I have to replace two tires on my flatbed trailer. Both the right-side tires went bad, are out of round, and one of the two has a tread separation. The two on the left side are fine. I think what happened is the two on the left were getting the evening sun for a few years. 

I'm going to go and get the two new tires today, but I wonder if makes sense to have one new and one used tire on each side, or to put both new tires on the right side. Maybe it makes no difference at all, the two on the left are not badly worn. Any informed opinions?

I guess I need to choose a better parking site for my trailers or get some of those tire covers. I really don't use my trailers often, but I need them from time to time.

[FUJIMO]

I just put 2 on an enclosed and they are running on the rear axle. For me it makes sense to have a new one on each side