Seating issues with plastic wheels On a Thule Chariot Trailer (back when sold as Trek), it came with the plastic wheels.  I got it second hand so I assume the tires are stock.  The tires are rated for 55 psi, but they slip off the wheel and cause blow outs (both out and about as well just sitting in the garage).  This happens on any of the wheels.  I can not find any damage to the wheel or the tire, so my current work around is using around 35 psi.  

Has my tires aged too much?  It has been garage kept.  While the tires do have some cracks in the tread, they hold up really well.  The sidewalls are kind of stiff so I can stroller around with it easily without air (these wheels have blown out on me in public before).  I notice that the tire is a bit more shiny than any of my newer ones.  Would replacing the tires with new ones prevent this from happening?  

Is a wheel change in order?  I see that the current models use conventional wheels.  The plastic wheels don't really bother me personally.  They are the side post quick release, with the release mechanism on the trailer itself and not like a push button in the wheel hub.
It's the plastic wheels.  Most mag(composite or plastic) wheels are only rated for 40 psi, no matter what the tire says.  No need to change out for metal wheels as long as you are happy with the trailer.