Upper bunk in fixed top?

[DerekH]

Hi guys, I have a 2001 smb with the explorer bubble top and the eb50 setup. There are cabinets around the rear and sides and I want to add an upper bunk over the lower sofa bed. It looks like I could just add 6’ strips of angle iron on the lower edge of the cabinet frames to support a bed platform but I’m not sure what the horizontal material is just below the cabinets. It’s covered with their plush fabric but I can’t tell if it’s 3/4” plywood or mdf like the cabinets. Obviously I wouldn’t hang a bed from mdf but I was hoping it was plywood. Anyone know what they used to build the sides where the roof was cut out?

Thanks
Derek