" writes:
Thanks everyone for the tips and considerations. Ill take precautions
on the box being airtight and will coat the wood with a moisture
barrier coating of some sort. Once i get this built and in
operation, ill be posting some results .

I think you are being penny-wise and dollar-foolish in trying to make
this a DIY project. Solar collectors are hi-tech engineering and even
small "errors" can result in huge losses in efficiency or even ruined
collectors -- it doesn't take much leakage to cause condensation which
in turn will destroy efficiency.

It has taken *many* years for big companies and experienced engineers to
get the engineering right so that the conversion is not only efficient
but stays that way for years. Even with the best of companies, they have
to offer long warranties because people doubt the ability of the
collectors to maintain their efficiency over the years of abuse from
hot, cold, sun, rain, snow, acid rain, grime, etc.

Remember that even making a lasting doubl-pane picture window was not an
easy feat and early failure was (and maybe still is) a common problem
until better engineering came up with more lasting solutions. Yet you
are designing something that will go in an even more harsh environment
where it will literally bake all day in the sun and then cool at
night -- repeatedly.

I can't imagine that a DIY solution would even begin to compete with the
know-how, experience, high-tech materials & seals, fabrication tools,
etc. that are available to an experienced manufacturer.

Seems to me like an exercise in frustration in the making...