How to down plate 5.5 ton van. what is mot class

Hi to All Members
I have renault mascott 5.5 ton.
I was going to register it as motorhome.
But this is more difficult than i thought.
I can not register it as motorhom because if i carry motorbike or quad bike than this is called by vosa as living van not motorhome.
How does it look with insurance? is this classed as commercial vehicle?
Because i carry no more than 500kg for my holiday and van net weight is 2700kg the question is if can i downplate the van to 3500kg and how to do this? where to go?
also when i downplate the van what mot class will be after downplating? class7?
For 5.5 ton van mot cost is 139 pounds. If is up to 3500kg mot cost 40 pounds.
In my opinion there are big gaps in Department of Transport regulating vans.
Even if people use the van as converted motorhome you have to pay as commercial vehicle with expensive mot and tax and insurance.
This is massive hit to working class people who can not afford new motorhome for 50 000 pounds.
Thank you All for your kindness and answers.
Wishing you All nice weekend
regards pete

Over 3ton but under 3.5ton is class 7

But the question is if can I down plate to 3.5 ton without any mechanical changes?
is it only VTG10 form I need to send?
Thank you