Attaching camper body to trailer

I am planning a Wanderer 10 build from Andy G.'s simple plans. One question I have, as a complete TNTTT newbie, is pretty basic: "How is the camper body attached to the trailer?"
The Wanderer uses two 1 x 6 boards directly over the trailer cross beams as key structural members, but what is the best way to then attach the body without weakening the trailer? Here's a detail from the plans for clarity:

Thanks and regards,
Matthew
The Wanderer uses two 1 x 6 boards directly over the trailer cross beams as key structural members, but what is the best way to then attach the body without weakening the trailer? Here's a detail from the plans for clarity:
Thanks and regards,
Matthew