What happens when you want to get loadall and tank to the same farm? Will there be something else to lift it on / off? Or tow the trailer and tank there with the loadall?
If you need to take the tank off without the loadall Stronga do something called the swaploada. If you specced the trailer with air suspension on got demount legs for the tank you’d achieve the same thing.
it would be rare we would be doing that - loadall normally only goes to stores at harvest to push grain on in winter to do maintenance jobs like trim branches and repair roadways etc. drills are serviced by the trailer we build with seed and liquid fert and we are all liquid N
I like the idea of air ( think along with abs etc it future proofs trailers a bit as legislation is only getting tighter) and we could easy make the tank demount like you say, I think the container twist locks are a good way to hold it down