Here is another little gadget that keeps the front suspension solid while keeping the forks extended. I had a buddy tell me once that bottoming out the forks for hauling was a not-so-good practice. Back then we were talking dirt bikes and I didn't bother ordering one of these.
Do you have any friends that ride Harley's? They should know how to secure a bike to a trailer?? HA HA!

EDIT: oops! I forgot that our feders travel with the forks so this would probably just mess-up the fender. I think the suggestion of putting a few boards under the frame would be a better idea! (Unless you are riding "fender-less").
