Welcome to the forum mhobby (& to the new Mrs too),
I'd suggest that you check the manufacture date on your remaining original tires & spare, and make note for your files.
The fact that your trailer is titled as an '08 model doesn't necessarily guarantee that the tires are also 2008's. For example:
if your trailer was built in late 2007, for the 2008 model year, the tires would also be 2007's (or older? Yikes!) -- you could be
even closer to that '5 yr mark' than you realize. Just an FYI.....
Enjoy your trailer, and Happy trails!
Terri, the Chevy co-pilot