Your probably right there Form !
Not too sure how you have connected them up though as they look pretty well fitted in there.
The 90 has the same rear as a 110 12 seater, just without the middle row of seats. When you have chance, would you mind measuring up 4 of the 125L tanks please. I can measure up a 90 then and see if they will go in like yours.
If it fits, then it will save a shed load of space as i was thinking of a 500 upright towards the front in a T shape to go over the arches.