Joachim, last night we were wondering how old your lad is, we figured somewhere around 10, but we could be very wrong as our memory of when we last met is fading. Photography eh, good on him.
For what you are doing, I pretty much think a tripod with your camera and bellows set mounted on a focusing rail, is about the only way to go. I helped with a project around 25 years ago using a Hasselblad with their makro lens. Once the correct subject magnification was realised, everything became locked, then you simply focused with a simple focusing rail. really rock steady tripod and either waiting for the wind to drop, or bring along your own wind shields.
The winds of late have been reasonably consistent between 5m/s through to 17m/s gusts, which is a bit of an ask once above 8m/s.
Mick.