Welcome to the forum! Sunline always said the max weight capacity for the Cabinet Bunks is 100 pounds. I have heard of people who have tried to "beef them up", but I wouldn't recommend it. The walls do not have much strength to them between the studs, so unless you mount some bracket directly to the studs, it wouldn't support the weight. If you do decide to use it as a bunk, make sure you have the piece of paneling over the cabinet doors so they don't open beneath the person in the bunk. If the bunk mattress and/or panel is missing, make sure you get something to cover over the cabinet doors.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR