Some of you mention trying to reinforce the bunks that come with your units. One of these might work as a bunk replacment for someone since they are rated for 300 pounds each.
Saves precious space. Perfect when you're sleeping in tight quarters. And, when you have some room to stretch out, it can be separated and used as 2 separate cots. Each cot is rated to 300 lbs. to sleep kids and adults alike. The powder-coated frame is strong steel and the cot is constructed of 600-denier polyester with PVC backing... both ensure years of use. Each cot stands 10" h. off the ground when used separately. When in the bunk position, there's 24" between them. Measures 72 3/8 x 28 x 35 1/2".
$50 at Sportmans Guide: http://www.sportsmansguide.com/cb/cb.asp?a=77336