Today was a good day - I decided to hell with the manual and its crypticness about the chairs, I was going to go in there with a wrench and get the damn things out. And I did! For anyone stumbling across this later, here are the screws I undid (note - clockwise):
The chair came off the base easily once I got those. Now I just have those black bases to remove on a day where it isn't absolutely chucking it down.
The spiders are still around. I stepped up my Raid game and sprayed the interior (patch test first) and got in all the nooks of the fabric. I have a depressing feeling that behind the fancy padded panels is a spider university, where they are learning how to successfully invade the inside of my van. I'll probably end up trying to remove some of them as a spot check to see if my theory is correct. I'm going to wait and see if any more appear before I do that though.
Other things... my friend gave me some carpet squares he had leftover, which will be really useful in making feet-wiping mats to keep the interior clean while I work on her. In addition (and this might gross some people out, but I've been dumpster diving for years and have lots of beliefs in reusing and recycling) I found a wrapped up rug in the apartment dumpster. The person had taken the time to plastic wrap it into a roll, and it had clearly been thrown away because they decided "you know what, we'll just replace this" - it was a bit 'dog' smelling. I've lumped it into the back of the van out of the rain, and will take a pressure washer to it this week to see if I can salvage it. It's a perfect red color to match the interior, and is the exact width of my van too, so I almost feel like this was fate!
Tomorrow we venture to a new mechanic with an excellent reputation, to see what they think of her inner workings. Hopefully my next update won't be full of doom and dollar signs.........