There were a few other design restrictions, like the trailer is un-sprung as solely a beach launching trailer, so the trailer frame is mounted on the axle to also keep the height down, it goes into the shed with about an inch or two to spare. Length wise the boat pretty much has no spare room with the draw bar up in vertical position. Width for storage was also marginal.
Storage is a problem that faces a lot of coastguard units, because they are often positioned beach front, other properties behind wont allow adequate extension to be made to existing buildings.
As a beach launching trailer you also need some clearance for sand and drift wood etc, it also needs to be able to be backed into the surf. So to build lower than the axle is also a problem.
As the boat leaves the trailer it can drop off the end if not deep enough, so you don't want anything off the back the jet unit to foul on.
Another concern we had with sliding drawbars is having any flex in the frame alloy on alloy could bind and also sand between the two plates could also cause a big problem.
Here are the images of the trailer and boat being put through its paces.
http://www.flickr.com/photos/amfboats/sets/72157622899989386/Here is an interesting video of RIB launch bow first trailer with a tractor
http://www.youtube.com/watch?v=wsGD2QWFryo these trailers are amazing so are their tractors. the trailer is set up with water tanks the engines are running as the boat hits the water.