I use my SIB on a T frame trailer with a bar bolted across pretty much from one wheel to the other with three rollers on it that are lined up to roll along the wooden floor boards that are on the inside the boat.
There is a big strong bar that the rollers roll on and are spaced using waste pipe tube, further forward on the draw bar I have a big carpeted flat bunk for the bow of the boat, then further forward of that I have an outboard bracket for my T 9.8 so no weight on the transom. I also have launching wheels so the trailer does not get submerged, I don't like walking too far with a loaded boat on just the launching wheels because it can be very heavy.
I also have frames to support two Optimist dinghies on top.
The boat is currently rolled up in the roof of my garage and the trailer is in a store at work so pictures are difficult. I did however snap this one today, I hope you get the idea - it works really well for me.