Thanks - some useful information to pass on to my boss. He drives a BMW 
The embarrassing thing is… it’s not even a proper van 
it’s a Nissan eNV-200, electric with an extra row of seats and… windows. This project started when we had a bigger, proper van, and several other things have changed since. The container is an insulated box to hold a metal canister that contains frozen blood samples (they’ll be in boxes…)
Here’s a picture of it taken previously
The reat seats will be well bolted down and that wee box aint goin nowhere … (apart from where you take it) so crack on drive, it will be fine… 
raymundo:
The reat seats will be well bolted down and that wee box aint goin nowhere … (apart from where you take it) so crack on drive, it will be fine…
My thoughts exactly.
Don’t over-think it. 100KG, that won’t move how you’ve strapped it there.
I’ve done less with 1000 kg pallets. 
And just as well it dont weigh much more as then it would be difficult to get it out with that back door arrangement which is a wee bit silly considering the van Is used for carrying goods imo.
Thanks everyone - I’ll try and explain it to the suits.
Getting the box to and from the van and the laboratory on the first floor is a whole other hurdle - but at least the tailgate keeps the rain off
