Trailers are available in galvanized or painted steel. We opted for the galvanized version. Painted trailers rust and chip after a few years use. Tongue extenders facilitate getting the trailer into deeper water. This is essential, especially with a wing or fin keel boat.
Trailers are available with single or tandem axles.
In addition to increased load capacity, tandem axles provide additional security incase of a flat. However, tandem axles mean twice the maintenance and maintenance cost. Instead of two tires and wheel bearings to maintain, there are four. We opted for a single axle. Most Catalina 22 trailers I have seen are single axle.