Putting support framework up would have to be done carefully to make sure you would still be able to access the valves for the water heater bypass and winterizing. Also, you would need to make sure you are not relying on the valences for support. They are not that strong. Given the curvature of the roof, there might not be much room up there when you are done. Just a sheet of plywood with support on the sides would not work. You would need to build a frame to support the plywood along the length as well as the width. Then you could use a thinner, lighter sheet of plywood for the platform to support the mattress.

Since you are talking about a 179, do you need a bunk because the dinette area isn't sufficient? If it is just because the dinette does not make up into a very good bed, check out my modification (see my mods link) to see what I did. It may be a better solution than trying to add a bunk. If you need a separate additional bed it might be better to frame up and add a bunk to the dinette area. If you made it on hinges to pivot down and be behind the bench seat back cushion while traveling, you would just need to have legs to support the front when it is pivoted up. The ottomans could serve in lieu of a ladder to access the bunk. The lower bunk would not have much headroom, but I think it would work out better than trying to put a bunk over the queen bed.

Edit: Do you already have a 179 or are you thinking of purchasing one? If the bed situation is not adequate for your family, you might be better off looking at a model that has more beds available instead of modifying a 179.

Originally posted by TacoTuesday Thank you for the information, it has given me something to think about... yes, I currently have a  179, and was looking for ideas to sleep an occasional grandchild without changing up the dinette every night.  I see that this is probably a project beyond my skills.  I appreciate your input.

You don't need to change the dinette every night. Remove the two corner bolsters and the center cushion and the remaining bench seat is plenty wide enough for a grandchild (or even an adult) to sleep on. Now if you are talking multiple grandchildren, then conversion of the dinette is better. My design makes it pretty easy since there are not the small cushions to slide off the table.

Summary of my changes:

1. Remove swivel mechanism from table. Install two posts instead.

2. Place a cleat on the outside of each ottoman facing the table side. This is used to hold the table when the posts are off. It also supports the sliding platform I made to hold the revised cushions.

3. Make platform from plywood with a board on the outside with rounded edges for comfort. This is used to stiffen the edge of the plywood to minimize flexing. It also makes it easier to grip and pull to slide it out. The bottom side gets gripper pads on the side nearest the center to keep it from sliding while traveling and slider pads on the side nearest the wall to make it easier to move.

4. Discard corner bolsters and existing center cushion. Make (or have made) two new cushions the same length as the existing cushion. One of these will be wide enough to come up to the bottom of the window. The other will make be to make the pair the same width as the existing cushion. When set up, this makes a 3/4 width mattress. Sheet sets are available for this width so no custom sheets are needed.

When the table is lowered on to the cleats, the slide-out will close over the top of it. This means that the table no longer needs to be turned upside-down and strapped to the bench seat. That is another big advantage as one can use the seat while traveling. It is nice to have a place to sit when stopping for lunch.

In comparison, it takes only about a couple minutes at most to change the dinette to a bed and unroll a sleeping bag.