Stay away from Carlisle.
Somewhere you can get 16" rims for the 6-bolt pattern you probably have. There is a wider range of heavier duty tires that can be found in 16" sizes. Just watch the sizes for possible clearance issues.
Lots of good info here:
Classracer.com - trailer tire threadCheck wheel bearings and adjust brakes regularly also.
I saw a significant drop in bearing issues with my old, heavy open trailer that uses 3,500 lb axles when I started using Amsoil's Series 2000 Synthetic Racing Grease.
Amsoil source & info site. 
