2 year update:
This cart has held up remarkably well.  I use it once a month.  I was worried that the wheels might not hold up to use on gravel roads. So far the cart has logged about 30 miles on the gravel and the wheels are holding up fine.  The cart has been exposed to rain and salty humid florida air and has had no issues.  
I do wish the wheels were a little wider so they were a little easier to pull through some of the deeper gravel, but it is not that bad.  Two guns plus 10 boxes of ammo and it pulls just fine.