I seem to remember that the 16 just about sits on the Infusion beams almost touching the deck inbetween. i went through all sorts of padding, but found 4 small car tyres to be the best. Not pretty, but if you bag them or wrap then - just the job.
I was towing behing a motorhome so the windage on the 16s tramp was not an issue. you could put the 16 on backwards if you like
I always tie the top boat TO the bottom boat rather than the trailer, this reduces the load on the bottom boat slightly