1442 Smoker Craft shallow-V structual integrity

Must first say that this forum has been more help in a short time than any other resource.  Most all my questions have already been answered in previous posts.  Keep up the good work!

On to the question:

I just bought this boat and it already had all bench seats removed.  There are 2x12s' laid across where, I'm assuming, the benches were with a deck made out of 1/2 in. ply.  We have already stripped paint and working on finishing it before moving to the interior.  Does anyone know if these seats provide side support?  I am putting a deck back in but I would like to do it right the first time.  If they do provide side support, do I need to secure the sides to the supports to prevent the sides from spreading or will they only try to squeeze together?

One more thing.  This being a shallow V (15 in deep), how stable should it be.  The original deck was about half way up.  Should this be a good height or do you think that this will be too unstable.  The guy I bought it from never said anything about being unstable.  Thanks in advance for any advice/tips/tricks that you may have for this situation.