Wow, thank you folks, for the warm welcome :). And for the advice and links!
I am not sure if I will be adding any weight. I am not doing tanks (black/grey/fresh), and the two rear seats I took out were about 100lbs each. Plus, of course, many fewer passengers. I am putting in a lightweight bed (2x2 frame and 1/2" plywood -- I am small) and assorted gear. In case I add more stuff later, though, I very much appreciate the suggestions of what will need upgrading.
I am not a skier or into snow camping. I am planning to live in the van in a cool but not frozen area for three months this winter. Likely 40-60 degrees and sometimes rainy.
It occurred to me to look at boat forums today, for insulation and condensation info. Steel hulled boats -- not that different from vans! What I have learned so far is that a thin sprayed on coat, like is used for sound insulation, is ok, but a thick coat (like in houses) promotes rust over the longer term. And that neoprene with a drainage plane behind it is ideal, but expensive.
Yes, I am familiar with the tendency of construction projects to be over time and over budget :).