I find the old stone buildings/towers in the swamp very useful to setup a small base of operations. Swamp is a pain to build in and for me at least, not enjoyable. So those old crumbly towers work great. Once you have some iron you can repair the stone. I just throw up some wood roofs and such as needed until I can properly repair it. They also can fit a portal, tight fit but it works. Then good to go. I usually sail my ore back to main base but once I used core wood & wood to build up and make a spot for a forge to make gear with since there were so many crypts nearby. The smelter was on an outside raised stone base (was on ground, smelted some iron, made the stone cutter, broke down and rebuilt).

And the various draugr villages make for quick outposts when traveling around.