How Dangerous are Weather Checked Tires?

[Walleye Express]

[b]I'm going to bet you that I have not put 100 miles on the trailer that hauls my Grady White charter boat around since I bought the boat 7 years ago. At that time, I had all 4 tires along with the wheel bearings replaced with brand new ones. But last spring when I brought it home for the boats spring cleaning and set-up, I noticed the tires were severly weather checked.

The tire tread is like brand new, but the side walls had more deep cracks than My 89 year old Grandpa's face before he passed away. Is this a serious problem that I should be concerned with? Somebody told me to first silicone and then put some black shoe polish on them, to put some moisture back in the rubber to stop the weather checking. Should I trust these tires, even though they are not put to any prolonged highway use?