Terra Firma rock sliders on 110 van

I ordered some Terrafirma rock sliders for my 2013 110 van. I specifically asked the seller if they would fit my vehicle and I was told they would. I’ve unboxed them and it looks like I will only be able to attach them using 2 of the 3 brackets.
Has anyone on here fitted rock sliders on their 110 van? Do I need to source an adaptor to allow the 3rd bracket to mount onto the chassis? Should I return these rock sliders and find a different set?

thanks

I looked into this very closely when bought for my 90. There are so many types out there that many of the manufacturers/suppliers don't really know what they're supplying to. I spoke with Dixon Fabrications who have the correct mounting points for the 90. Could these 110 tree-rock sliders be a better fit for you...?

https://dixonfabrication.co.uk/110-ROCK-SLIDERS-

If not, why not make up a thick alloy L-shaped bracket to mount between the Terrafirma units and the rear bodywork/near to the rear wing stay? L-profile alloy @5mm thick is very strong and is readily available online/from eBay https://www.ebay.co.uk/str/emg-metals-and-fab/Aluminium/_i.html?_storecat=20709141010 or https://www.metals4u.co.uk/materials/aluminium/aluminium-angle?shape=70600&thickness=71264

Thanks v8250. I’ll make up a bracket. I had looked at Dixon but their lead times were too long.
I was also told that the terrafirma rock sliders I ordered would be a good fit so that is why I went ahead with the purchase.
I’ve since discovered that many people only mount rock sliders using 2 brackets so if I can use a third then that’s a bonus.