It may not be normal, but it isn't uncommon either. What is the date of manufacture for the tires (it is on the sidewall)? It is not uncommon for tires on a new trailer to already be 2 years old when you purchase it as they are purchased in bulk and sit in inventory before they are used.
I replaced the tires on our fifth wheel last year. They were 4 years old from purchase date, but 5 1/2 from manufacture date. Tread was still in good condition, but like yours the sidewalls were developing cracks.
Glenn & Beth (Dad & Mom)
David & Audra (12 year old twins)
2006 Dodge Power Wagon (Adventure & Tow Vehicle)
2006 Rockwood 8281SS (Home away from Home)