I'm only at the early planning stage but figure a Leyland DAF could be the right beast. I also think converting an existing 'bolt on shed' (ex MOD Comms Cabin) might be the easiest option but I'm a little confused why some owners go to so much trouble in fabricating a body that allows the chassis to fully flex. Obviously this must enhance it's off-road capability but I'm curious to know how the flat bed 'bolt-on' option deals with this? For example is it necessary to factor in a lot of tolerance in the fitting out? Or maybe the off-roading gets compromised. Will that be such a big deal if I try keeping to roads. If anyone can advise I'd be grateful. Thanks.

the chassis are designed to flex a little, and if the mounts are all rigid, then the body will be forced to "flex".
If you are looking for trucks, worthwhile looking at the mod dispersals at Witham. easy to deal with when I bought my 4x4 ambulance.
Leyland Daf, 45 / 150 4X4 Flatbed, #40349 - MOD Sales, Military Vehicles & Ex MOD Land Rovers for Sale

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I'm reasonably sure that there was a long and very informative thread about this topic a few years (3 - 4) ago, 4x4 pods for Unimogs I think was the main discussion.

There s plenty of websites that have advice by self builders and professional fit outs on a whole range of 4x4 truck chassis.

If you are going to stick to roads because of the body why bother with a 4x4? a regular campervan would be just as good imho.

One of the main reasons you see conversions is not so much about the ability to flex its about the size of the cabin and the weight especially for those using the ex-mil unimogs which only have a 2T payload where the bolt on military cabins take up half of that empty.
The ex-mil cabins can be pretty low for tall people or if you want high up bed, they simply do not allow as much space.
If you go on youtube or google you will see as many people using bolt on ex police or military cabins in trucks with a higher payload as fullon custom built and they do just as well offroad. Heres 2 trucks one with loads of twist and a custom cabin and one with I think an ex mil or police cabin. First link shows the cabin on the daf being converted/built
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Khowarib Gorge - YouTube


Max the Truck - munromobile - YouTube

The flex thing is more to do with the chassis is designed to flex , when fixing a box on you need to take this into a/c as the box wont stop the chassis but the chassis will destroy the box . With a existing mil mounted box this will (should have) all been taken into a/c . They do tend to be a bit on the heavy side for what they do , you need to try and get laden and unladen weight and see if that gives you the capacity you need. Mil trucks do tend to be conservatively rated but you still need to operate within the law . HTSH

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2010-06-27 gives a good rundown on building a 3 point body mount for a Mitsubishi truck.

These might help too - not actually the one I had in mind which I saw a year or 2 ago

OverAfrica - Vehicle choice

Leyland Daf 45/150 4x4 | Trucks | My Wheels

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This is my take, for what it’s worth, on the OP. Many (me included) go the ‘fabricating body’ route to enable more control over the weight and dimensions, and to have the flexibility to accommodate their exact requirements. There’s nothing wrong with a ‘comms cabin’ conversion, but you are kind of stuck with the dimensions and weight. Forget getting under 7.5 tonnes if you go this way.

Owners fabricating their own body don’t always take the torsion free sub-frame route, but instead build directly onto the standard flat-back bed. The standard LD T244 bed is itself very rigid and is attached to the chassis with a combination of rubber mounts and bolts (at 8 points) and so does allow a bit of chassis twist as a standard feature. A ‘comms cabin’ is very heavily built and any tiny amount of flex that does reach it through the standard bed will not trouble it at all – under any circumstances. They are engineered to take a hammering.

Likewise, a self-made box, if very strong, should not have any difficulty in coping with the torsional stresses it receives. A major caveat here is that for extreme / prolonged / unsympathetic off road hammerings, then a self-made box on the standard bed - if not as strong as a ‘comms-cabin’ – will probably eventually fail. Don’t forget that as well as torsional stress that it will also be subject to shock / vibration / and a general shaking about passed up through the suspension.

For mainly road and sympathetic off-road use then a self built box on a standard bed should last the course. Indeed, I’ve put my trust and money into this solution myself. Login - Trip Truck for more info.

For extreme, prolonged, or thrashing-it-off-road use, then it makes sense to use the ‘comms cabin’ approach, or to rip off the standard bed and build some sort of torsion free rig to support a self made box.

It is seemingly a bit of a black art and there is no one foolproof solution, and probably no-one out there that can give an absolute definitive answer. Whichever way you go there will be compromises.

One thing for sure is that if you build a box directly onto a truck’s chassis rails then it / the chassis / mounting points will very probably fail in even mild overlanding conditions.

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