I did something similar to this last year, but without the travel goal (just trying to get myself to move around and work outside more). Instead of mating the keyboard to the base, I attached some larger magnets to the bottom of the keyboard by setting them into a custom aluminum bottom plate (also from SendCutSend) and made a flat desk surface out of ferromagnetic steel.
https://ianthehenry.com/posts/kyria-build/bespoker-aluminum-...
One advantage of this is that I can move around the keyboard halves freely, angling them differently throughout the day. Which is also sort of a disadvantage, but they stick pretty well in place if I'm not trying to mess with them. I can also attach some other things that I slapped magnets on (mostly a mechanical pomodoro timer that I use for writing).
https://i.imgur.com/S0bstNs.png
I experimented with some alternate keyboard mounting strategies, but didn't find anything that made a big difference.
https://i.imgur.com/ohNWhhS.png
This is my second magnetic keyboard lap desk prototype. My first was far too heavy, so to reduce weight I just bent a piece of sheet steel around a piece of cork (the sharp bends add a lot of rigidity). I think the next one will be tented a bit... SendCutSend does bending now; I bet I could laminate steel to a thin aluminum frame...