There are a few different Trax cart versions in circulation. The latest has "S" shaped legs for a wider wheel base, the tougher wheels shown on the right above. They are easily distinguished by smaller hubs and no traction bars on the tire surface. It looks like this (shown on a different boat here):
As Matt says, the legs should be long enough to slip all the way through the scuppers and latch as shown here:
There is an early version of this cart that has legs about 1" shorter -- works for most boats but is not quite long enough to latch on the PA. Looks more like this:
This early version may also have lacked "post collar clamps" (subsequently provided at no charge to PA owners). They are the black donuts on the legs.
Here's a review on the new wheels: viewtopic.php?f=11&t=16179
See your dealer to get the correct cart. While either set of wheels is rated to haul your PA, these larger capacity wheels will make it a lot easier.
PS: I believe these wheels are more expensive than the older wheels. If a warranty exchange doesn't work out for you, you can buy the new wheels and use your existing frame to save some $ -- keep the old wheels as temporary spares (you probably won't need them though).