Weight capacity when not in motion?

I wouldn't worry about it.  There is a big difference between static loads and dynamic loads.  When they say you can't load a trailer with more than X pounds they've taken into consideration that those X pounds will be several multiples of X on the frame as it bounces down the road and hits potholes.  Just make sure you have the front stabilizers down and don't go jumping up and down all at once when your favorite hip-hop song comes on the radio.