Sort of missing the point isn’t it? Winpro doesn’t have his bolted in therefore it’s not a modification.
Yours is bolted in and you’ve declared it a modification.
The argument is where does it say any load is a modification.
Why should a windowclener be penalised for carrying 650kg of water and not a builder carrying 650kg of bricks?
In your argument a windowcleaner will not be insured because he has a tank. So why is a builder insured or anyone who carries pallet loads of heavy items?
That's how I see it, legally. However two points.
1. If you fix a reel or a pump then that would be a modification.
2. Although in my case I believe that strapping a full 650L tank to the vans lashing eyes would be legal I wouldn't think it as safe as bolting it in a frame through the floor.
So because I have done this then I need to declare it as a modification.
If I take the risk of strapping my tank to the lashing eyes I still believe the other paraphernalia bolted or screwed in place like a second battery, pole tubes, pumps, reels etc. obligate me to declare those modifications.