Rathgar
I'm not sure how a type certification would work (or if it's possible).
As for the GCM - there is no GCM currently existing and so you (and the authorities and insurers) have two choices -
1. Use the military recommendation for a 1200kg towed weight (would probably still need trailer brakes on civvy street) + 3200kg GVM = 4400kg as the "existing" GCM and then to engineer a mod for each vehicle (perhaps becoming easier with precedence).
or 2. Using data for a similar vehicle as per either the NVD or Operators manual - all of which allow a towed weight of 3500kg or greater (up to 4000kg for a 110 Isuzu "cab chassis").
I have chosen number 1 because it is rigorous and wasn't much extra effort as I was also changing the seating capacity and needed a mod plate anyway.
And for the hair-splitters - you need to consider the tow-ball down weight when you calculate the towing vehicle load capacity so GCM is actually less than 3200 + trailer weight.
If the receiver tube were higher then it would need to have more rear-wards overhang as (AFAIK) only the 21126 TBM gives 3500kg with a short shank that wont foul the spare. A longer overhang is detrimental in terms of towing dynamics. This design was the best compromise for my situation.
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