Re: good idea or bad one
Here's mine on my race bike.
Cut and welded the pan out of thin sheet metal, glued a mouse pad for the cover, welded the struts to the frame (which have a flat bar welded across the top,) and the seatpost has a flat bar welded to it so the pan bolts on.
The back speed hump will bend if you put weight on it, but the seat area has a folded lip so it's strong enough for my 135lbs of pure muscle.
Not comfortable at all for cruising, but I don't notice when in my leathers at the track.