I failed to mention, I ended up doubling up on the rubber washers. The ones I bought on Amazon--a variety pack--seemed about as thin as the squashed original washers. Right or wrong... it works.
For the curious, the power station mentioned is the EBL MP330 Portable Power Station. In my extremely limited testing, it's quite good for my needs. (The link is an Amazon Affiliate link. Your purchase results in a small commission for me, which is much appreciated!)
Once again, my blog has been cursed. I finally typed up something to post and PostHaven is having errors uploading the scan, at a variety of sizes and resolutions.
It's tempting to pull the plug on this blog altogether, but let's try this third party image hosting site: