I like that low-profile platform rack, looks properly made too.
Who makes that? I'd go as far as buying and adapting that if the price was normal and dims and attachment points were in the ball park.

One idea I've had, based on how I interpreted the vaguely similar 'Angolan' rack, was adding a same ø bar above the bottom main tube (welded), or behind and above it, as pictured below (easily clamped).

That way, for less rigid soft bags you can slot in (or hinge down) a board which will be cantilevered off the added back bar and platform edge, giving you width support when needed. Should you fall or need slimness (to get through a hotel door), the board will either slot out, flip up or just come away, and should it break is the sort of thing that's not hard to replace on the road. Plus its use is optional anyway. The Angolan rack works in a similar way, but uses fixed tubing - bend prone maybe but also less likely to come away and get caught in the spokes as a loose board may do.
Tubed rectangle or wooden board, I like the idea of a cantilevered, hinge-out platform.

I know what you mean about thinking a lot before taking action, especially when resources or a location to take action are limited. You want to get it right first time. I like the idea of clips permanently attached to the pillion peg area and rear of a frame to fix the bottom of the pans and stop them swinging. One less thing to fiddle with and those clips are light to carry as spares, and easy to replace, even with a knot if you can't sew at the time.

I'm not sure how I could use those ally clamps which seem to be hose guides rather than weight bearing. Anyway, as mentioned I've ditched the clamp assembly idea and have nearly finished my slackrack which has been fun to figure out but could get thrown in a skip if something better comes along (or if it falls apart on the first speed bump...). All would be so much simpler if a proper luggage rack was available for my bike that wasn't set too far back.

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