Been looking very much into these boxes. And I've uncovered a few bits of information.
The are NATO ACE Shelters. They come in different sizes, ACE I, ACE II, and supprisingly ACE III.
There are a number of companies who produce them, but they are all built to the same military requirements - Allied Command Europe's Standard Shelter Technical Specification 6516/SHCPR/8
Roof load -
Snow and ice 3660 N/m2. The roof shall be capable of withstanding a concentrated load of 3.5kN distributed on a 0.25m2 area (0.5m x 0.5m) anywhere on the roof
Floor load -
The floor shall be capable of carrying a distributed load of 5kN. The floor shall be capable of carrying a concentrated load of 10kN distributed on a 0.25m² area (0.5m x 0.5m) anywhere on the floor
Temperature xtremes -
• Operating: -40ºC to 55 ºC plus solar load.
• Non-operating mode: -45ºC to 70 ºC
Heat transfer coefficient -
U-factor = 0.28 . Designed to meet requirements of NATO STANDARD #6516/SHCPR/88
RFI/EMI -
The shielding shall provide at least 80 dB attenuation to electric and magnetic fields and plane waves in the frequency range from 150 kHz to 10 GHz when the shelter is tested in accordance with MIL STD 285.
Watertightness -
The shelter shall be capable of being immersed in water to a depth of 500 mm, measured from the bottom of the skids, without ingress of water inside the shelter
C-Rails -
Each shelter shall be equipped with C rails for the fixing of internal equipment.
Quantity:
1. ACE I Shelter
• Side and front walls: 3 rails
• Floor and ceiling: 6 rails
2. ACE II or ACE III Shelter
• Side and front walls: 4 rails
• Floor and ceiling: 6 rails
Standard features -
• Skids: 3 full length replaceable type
• Roof Access steps: 4 folding steps in sidewall and one roof handhold
Transportability -
Transport by Truck:
The shelters with payload shall be capable of being transported over cross-country terrain by military vehicles without sustaining any damage.
Corner fittings -
The shelter shall be equipped at its top and bottom corners with fittings that comply with recommendations ISO 1161-1976 (Series I freight containers – corner fitting specifications). These fittings shall, by making use of suitable slings, provide a means for lifting, towing and tying the shelter.
ACE I
External
H 1825
W 2050
L 2900
Internal
H 1635
W 1885
L 2735
ACE II
External
H 2075
W 2200
L 4250
Internal
H 1884
W 2034
L 4084
ACE III
External
H 2075
W 2200
L 5000
Internal
H 1884
W 2034
L 4835
NATO I
External
H 2110
W 2080
L 3810
Internal
H 1907
W 1933
L 3573
NATO II
External
H 2110
W 2080
L 3810
Internal
H 1882
W 1933
L 3573
NATO III(1)
External
H 1780
W 2000
L 2160
Internal
H 1577
W 1853
L 1923
NATO III(2)
External
H 1886
W 1747
L 2340
Internal
H 1683
W 1600
L 2103
Now to say that these boxes are coming up cheap is an understatement.
I've priced up building a box for the camper. The steel framework will cost in the region of £500 and the alloy sheeting for the outside £1300. That's no insulation and no interiour skin, no door fittings etc...
I'm looking at paying around £1200 for an ACEII which is fully insulated, alloy skin on both the interiour and exteriour, military spec build quality... and guess what - nearly exactly the same dimensions at the camper box I was planning on

:thumbsup:
Guess who's waiting to hear when the supplier has the next one in stock (2 - 3 weeks he recons).
