Fully run in and going strong!
Join Date: Oct 2014
Location: Mullion, Cornwall, at present
It all comes down to what the replating states...
In order to be replated, in the UK at least, you may be required to do an approved mod to the vehicle, which may be as simple as uprated springs but could also involve extra airbags and chassis bolster brackets. You are allowed weight in the tub (up to 1t typically) plus up to 3t or 3.5t of towed weight (depending truck), and usually up to a GTW of 6.5t or 7t, depending on it being a D40 or NP300.
The worst case is when you tow with standard tow ball/bracket because this puts a huge stress in terms of a vertical torque on the chassis, owing to it being a huge lever. Many people seem to break their chassis by not understanding this as a limit in its own right irrespective of weight in the tub. Nissan tells you the limit for you model, but it really does depend on how much the tow bars sticks out, which is a grey area. Bear in mind that an extra 6" is probably 10% more vertical torque, irrespective of the weight loading... Go figure....
Where you have a 5th wheel, the nose weight is precisely over the rear axle in the tub by design (5-800kg is typical, and assuming the fitter is not clueless, which has happened), and it does not lever the front wheels into space, like if you are using a tow-ball.
If you buy a UK, type-approved 5th wheel, the weight and weight distribution is going to be legal for UK and EU. If you buy a US import 5th wheel, you have to do you own sums, as not all suppliers are entirely up to spec with many of the regulations. In all cases, you have to ensure yourself that the total load in the truck and the trailer does not exceed the the max GTW, -or- the max plated loading on the (rear) axle, -or- the max allowed weight in the tub.
2014 Nav D40 V6 ('Herman'), towing Celtic Rambler ('Priscilla'), the de-facto luxury and quality 5th wheel from Wales.
The plural of anecdotes is not data. Anecdotes however, are better than hearsay