We are looking at building single family seasteads.  In general there are floats/legs going down into
the water (often like a fat wing so can move through the water better than a round cyliner) and a living 
area above the water.    To keep costs down we are looking at
getting the legs made in China and so the designs all have them fitting into 40 foot containers.

The question I would like your help with is how the above water parts should be constructed.

Much of the stability of most of our desings come from having large width, like a triangle
80 feet on a side, and we expect these to be truss structures where the parts can be made
in China and then assembled at a shipyard in the Caribbean, just bolted together.
I think of the Eiffel tower and lots of simple beams bolted together.
So the first question, aluminum is softer than steal and I worry that bolting beams together
will not work as well as with steal.  Can we make strong truss structures with aluminum beams?
Or is this a strong reason to use duplex stainless steel for the truss structure instead?
Doing both the floats/legs and truss in duplex stainless steel seems an interesting option.
The cost of the solar, batteries, plumbing, electrical, etc does not go up and you end up
with a structure that last much longer.  A seastead does not have to pay for land so paying
to have a secure foundation platform may be reasonable.

The second question is how to make the living area water proof.   There will be times large waves
splash against the living area.  It would be nice if pieces could be bolted on but is there a
way to do that which is both low cost and reliable long term?  Or will we need to plan on
having a shipyard that puts all the pieces together do some aluminum welding for the water
resistant skin of the living area?