First, let me sign the waiver of liability since I'm sure the manual says to empty all weight from the boat while launching/trailering.......

I'd do it. I wouldn't see a problem leaving 300#'s in each rear locker. I assume we're talking non-highway speeds/etc? You may need to put the trailer a little deeper when launching to compensate for the stern sitting a little lower in the water, not sure, but something to watch for.

Now, on to the important question......what new surf are you looking at??