as to the ones you listed Allen, and Instep , I have no experience , with those on a Brompton.

you may have to fabricate something to bolt down, under that left axle nut and then have a separate hole drilled

In, say a piece of steel 1/8" thick , to then attach the piece, onto which that the tow bar attaches ..

folding the bike can only happen after removing the trailer ..

so think about making, or having made, a combined piece,

that not only fits the trailer hitch , but also a prop/Kickstand ..