Hey Jorhyne – Don’t take this personally but you need some balls!
I mean of the Roadrunner kind as seen here:
http://www.hobiecat.com/community/viewtopic.php?t=7223
They act like suspension and protect the scuppers and hull from deformation. I swapped the tennis balls for solid soft rubber balls. Just make sure the cart uprights extend all the way through the hull.
The Hobie Trax cart isn’t perfect but when fitted with wheels more suited to hard surfaces I find it OK. I have had to re-weld the axle to the uprights though when the original welds broke.
I do wheel my Adventure (and sometimes AI) probably a bit further than most –about 4kms twice a week.
The problem is that the Wheeleez wheels are really only designed for sand and as Drew posted the correct pressure is crucial. You can use them on hardpack but the drag is terrible. I posted about swapping the balloon tyres for standard wheels here:
http://www.hobiecat.com/community/viewtopic.php?t=8956
If you want to make your own cart look at the cart I made out of bimini tube and fittings in the above post. It is still going strong!
BTW -I have since added large flat stainless washers under the balls to stop the lower ball deformation seen in the above pics.