We have the smell too!
We have the same smell occasionally. It usually is the bilge. Since the shower and icebox drain into the bilge on the 29.5, sometimes you get some nasty gunk building up in the bilge over the week if you aren't using the boat. believe it or not, soap rots and stinks. Easiest thing to do is pull up the sole boards and flush the bilge with a hose until it is clean. Then drain as best as possible and use a good bilge cleaner. One of the organic or enzyme types are very good.The other cause could be the holding tank. We had this smell in the aft berth too. This year we tried the KO product and it is great. I can't believe how well it works to reduce odors versus masking them as with the "Blue Stuff".I would not imagine your odor is a "chemical" but and organic caused by either the holding talk (or a holding tank leak) or the bilge.Good Luck!