Re: What can I build in this spot on my boat?
Yes you could easily modify that area back there any number of ways...
I like your idea of seats+doghouse, with storage under the seats...that could give you a bit more deck space...you could build in a cooler with insulation, you could add additional storage for those extra life jackets, if you like to fish, you could add a live well, the possibilities are only limited by your imagination, needs, wants, and of course...budget...
You can screw into the boat, it's just that is not the most secure way to do it, and it could cause water intrusion issues...
If you are not averse to doing some grinding and glassing, the best way to make any additions would be to fiberglass the new parts in and even provide a place to solidly screw or bolt in future additions...of course it is a little more involved than that, but with the knowledge base available here...anything is possible...
The best suggestion I could give you is to look around this forum, A LOT...read through some stuff, use the search feature to look for ideas...put in search terms like..."Doghouse", "New Seats", etc. etc...Look in the "Boat Discussion" threads...eventually you'll start to see what you want to do...There are literally tons and tons of ideas and info on stuff you could do back there...
Do some research, make a plan of what you want to do back there, ask a bunch of questions on how to do it, and we'll be here to help you out any way we can...
You can use free cardboard and tape or a hot glue gun and make up some really detailed mock-ups of what you would like back there, then turn that into reality, once you come up with a design...
Take a look at what one the guys restoring his boat is doing...
http://forums.iboats.com/showthread.php?t=523969&page=2 ... look at posts #701 and #721...
Have fun coming up with a creative and useful addition to your boat...