I’d found the Drizz Developments via Google, but haven’t been able to watch the video yet.
I have been thinking though that whether it’s DIY or not depends on the space and the tools etc you have available - specifically a hoist or ramp to help separate the body from the chassis; and then a forklift or similar, to lift the bare chassis on/off the trailer.
If you were able to separate the body and the chassis; and had an engine crane, I don’t think it would be that far from DIY.
Once I’m mobile again, I’m going to get in touch with an underseal/rust treatment place and see what they reckon their chemicals can do. I’m told it was ca. £600 to prep and treat a Defender, and that’s a bit cheaper than £3000 to do the chassis - which I suspect is probably a bit low away up here.
Edit - OK, just watched the first two videos, and I’d agree that it’s at the furthest end of the DIY spectrum. It doesn’t really seem technical in any sense, just a bit involved, and lots of heavy lumps to shift about. If I’d a ramp and a hoist then I suppose I might think about it more seriously in the future, but for the moment this is definitely not on the agenda!