4,000 Kg and Euro 6 is best?

Hiya, newbie post.
I've been toying with the idea of a van conversion for yonks, partly so I can work around the country and not hand over hefty hotel bills.
As we probably all agree the VED taxation system is chaos. Any electric vehicle owner is probably feeling well uncharitable towards the government since April, it's not like public charging is cheap.

So I was thinking, to get the lowest VED rate possible for anything other than a pedal cycle (soon them too will be taxed - call em cynical) if one obtained a modernish van which is both euro 6 and plated at over 3,500Kg i.e. maybe 4,000Kg, then when you convert it, it will still be euro 6 so ULEZ exempt, but being over 3.5T it should attract the lower VED rate for campervans. i.e. TC 10 instead of TC 11.

Any flaw in my thinking?

And how small an added window counts as one of the three? I'd prefer to keep the windows modest and fit them between the internal body posts. Also maximises the freedom to install fixtures like shower, toilet etc where I want them.

They don't now have a minimum bed count do they? Thought just two permanent would do to save weight, with a design allowing for 2 more added temporary if and when taking the family hordes with me.

Does the typical rear door of a van count as the required door?

I intend covering the roof with solar panels so no sunroof.

Cheers

If you want it reg as a motorcaravan then look up the rules etc bed size water tank cooking waste tank windows etc, some rules have been dropped like stickers all over the outside etc, good luck.