Yeah, i get how the frame sits, just not how its fixed to the van...?
Ok, the front member of the frame is the width of the van, it cannot physically go beyond the pillars, in effect its like a bulkhead. I fitted a metal bracket to either end and bolted it into the existing holes in the door pillars. That stops any up or down movement. It can't go anywhere even if you shoved a jack under it. The only thing i can't confirm is which will give first, the pillars in the van or the 3x3 timber, if i have a high speed shunt i'll let ya know !!
Although really i suspect it'll all just sit where it is.
Don't forget when you see these crash test comparisons you're looking at an IBC which has a water tank not much stronger than a balloon, and a flimsy aluminium frame. Oh, and also you know i'm just going to mention again that the Pro Fit ones bolted through the floor will potentially write your van off if they buckle the floor. Your "system" will be sound though !!!
The potential damage to the chassis/subframe of the van in the event of an impact (not necessarily high speed) with a bolted in system is a very good point, and one reason why i wouldn't bother with one.
However, to my mind, the whole concept of trying to keep the tank rigidly secure in the event of an impact is fundamentally flawed. Trying to stop that much energy with no movement is virtually impossible. Think of how car safety has progressed, it used to be the case that cars which were built like tanks were considered the safest, think of old volvo's. But of course we now know that the car HAS to deform, to crumple around the passenger cell, dissipating the force of the impact, as opposed to transferring it all to the occupants. If a tank is strapped in (properly), in an impact, the combination of the natural stretch which will occur in the straps, combined with the bending and distorting of the tank will, to my mind anyway, provide a similar, albeit rudimentary, equivalent to a 'crumple zone'.
My next van will probably be a citroen dispatch/fiat scudo/peugeot expert. I will be strapping the tank in, but the reason for my choices is that there is also a built in 'backup'. In the vans i mention, at the front of the load bay, there is a 'step' up from the floor of the load bay, to the floor of the cab. This looking at pictures i would guess to be about 6"-7", and is in fact a major structural cross member. If you have a tank in the back which is strapped down (that is to say, wont jump up over the step), even if it moves forward, it wont get past that step!.
But lets just hope none of us have to try out how well our tanks are secured in a high speed shunt, as i suspect it wont end well for any of us.........
Drive carefully peeps