I'm afraid I have fallen out with 'Really Useful Boxes' - they're great for the home/office environment but just too fragile for camping and trekking in the Landy. If the bases don't crack the handles do. I shifted over to Euro/ISO standard boxes from Solent Plastics some time ago (available elsewhere as well); they are much much stronger, come in a variety of sizes, lidded or open, and all stack locking into each other making it easy to make the load secure in the back of the vehicle.
A fraction of the price of the Wolf boxes often used for trekking but just as good IMHO
See:
https://www.solentplastics.co.uk/stacking-plastic-containers-boxes/
and:
https://www.solentplastics.co.uk/stacking-plastic-containers-boxes/hinged-lid-euro-containers/
as examples
Not used the Solent plastics stuff but will take a look, next time I need something like that.
IME, the RUBs are OK for domestic use and for occasional expeditioning but like you, I have found them a bit too fragile for long term use but TBH, I’d probably take them over the wolf boxes which are a bit small, (unless they have improved since I last looked at them), have flimsy catches and despite being marketed specifically to Expeditionise your Landy, are not dust proof - the back of a Defender is a magnet for dust and sand. The ammo box image appeals to some people but there are better solutions.
IMHO the “gold standard” for expedition storage is the aluminium Zarges box, light, strong, available in a vast array of sizes, stackable and fitted with an o ring to make them water and dust proof and (to a degree), vermin proof. The downside, the eye watering cost of them new! I was lucky to get 8 of these for £30 a pop at a Landy show many years ago and built a storage system for my 110 around them.
https://www.zargescases.co.uk/product/k470-aluminium-case-60l-2/
They do occasionally come up for sale on the Bay of E etc (esp the half sized medical kit ones) but people seem to have cottoned on to their value and I have never seen them for the price I paid since.
I ended up removing the middle row of seats and fitting a box either side of a fridge. They can still be used as a somewhat uncomfortable seat for short journeys but probably not recommended on the road in the U.K.
After three and a half years of near constant bouncing around in the back of a 110 they are a bit scuffed and scratched but functionally as good as new.
A great solution if money is no object (and people do spend silly amounts of money on expedition and off-road accessories) or you get lucky - and no I’m not interested in selling!
Another lucky find I made (which again I’ve not seen since) were some heavy duty fibreglass suitcases about half the size of the Zarges boxes and which originally contained the sights for a Milan antitank missile, complete with lens cloths and brushes. Similar to this one but smaller, in mint condition and only a tenner.
https://www.ebay.co.uk/itm/Ex-Milit...344735?hash=item2f30eda99f:g:S-cAAOSwA2Fc4oFt
Stripped of the foam padding and painted in some less “warry” colours to conceal their origins they made excellent storage boxes for heavy spare parts etc. Highly recommended if they turn up for sensible money.
To misquote Dirty Harry, “Everyone has an opinion”
I hope the OP finds something that works for them!