I can't believe it's been almost a month since I updated this thread. Most of the time was spent building (and rebuilding) the rudder structure. This is what I ended up with:
It's mechanically quite sturdy in 1/35, so it would probably be as sturdy on the real thing.
Here it is, almost finished. The rudders are linked with some PE chain that I made years ago (for a 1/350 scale ship). The linkage works, although it is fragile.
The Aerosan is attached to the deck with baseplates from some railroad ties, leftovers from a BA-20 armored car kit that had an option to mount it on a rail. The deck hatches are Stryker leftovers from the AFV Club M151 Protector kit. The treadplate at the bow is a raised detail decal from Archer Transfers:
I skipped a step and painted the hull with Vallejo Russian green; I had wanted to show a rusty hull underneath, so I had to go back and remove the paint. Unfortunately I didn't seal the wooden cross member under the deck and I missed the edges of one of the deck planks, so it warped badly when I got the deck wet. I removed the deck, trimmed and repaired what I could and put it back together.
Then I painted the hull in a dark reddish black undercoat, applied some salt, then painted it with Russian green. I removed the salt with a wetted brush and accidentally pulled up some of the treadplate on the bow. That's why it's "rusted through".
The side view shows the new rudder control connections, as well as a fuel pipe (for extended missions). The rudders look fairly clean because I accidentally placed the Russian stars upside down, so I had to strip and redo them:
I still have to add some vodka bottles, some deck ropes, poles and maybe a crew. I'm thinking of using the white foam board as a base for a wetlands diorama, with maybe the aerosan beached on a riverbank with the crew receiving instructions from an officer.