Ok so having read your other thread (as you suggested) I think I'm beginning to see what's going on.
You paid $105,000 Au for a fiat based Jayco built camper van, which turned out to have been used as a demo model and had some minor damage and you eventually negotiated a completely new motor home.
After a few months of ownership you found a problem with water ingress into the engine bay which had left some corrosion, this is a known problem for which fiat already have a fix.
When fiat attempted to undertake the recall you requested to take pictures of the pre repaired state but ultimately gave authorisation for the work to go ahead, they went ahead with the work before you could take pictures (for what ever reason) and threw a tantrum about it in their dealership which brings me to my first point.
If they are repairing the problem as per the instructions from the manufacture and it is not costing you anything why Did you need to take pictures? This seems pretty odd. Anyway they did their fix.
You say that there is corrosion and rust in the engine bay but you show me any van car truck what ever after a few months on the road that doesn't have this? No engine bay Is water tight, I appreciate the frustration at the damage caused by water dripping on to the top of the engine but it really is only cosmetic, ranting and raving about other peoples vans isn't really going to help you.
You then say the fiat dealership did some damage to the grill and what-not, which you went back to them to complain about further, which clearly resulted in an out of control argument as you were chased off the premises and banned from ever returning. Perhaps your reaction to them undertaking a simple recall without you being given the opportunity to photograph the engine bay did little to endear them to you?
Something about the aircon broke down which again I assume you got fixed under warrantee etc but you don't say if this was fiat fitted aircon or something installed by Jayco during the conversion, either way it's fixed and that's what a warrantee is there for.
Right now you move on to Jayco ranting and raving about the brothers who run the company etc etc all irrelevant blar blar blar I don't care. But what you do say is that there is a problem with the sealing in the roof that has caused rot? Obviously a problem but Seeing above you say the motor home is now four and a half years old I'm guessing your no longer covered under warrantee? No I have to say this I sympathise with because clearly the problem has existed since it was built, however you have to Prove that after all this time and with 20,000km of use that this isn't as a result of damage incurred after you bought it for instance you twisted the van on rough uneven ground and broke the sealing letting water in, you say it's well documented but documented by who? Other owners who have problems with leaks? Or Jayco them self. Obviously if it is Jayco they have an obligation to put the vehicle right, you mention "numerous other fault" but don't say what so can't really comment but your motor home is no longer a new van it's nearing 5 years old! Given your attitude towards the fiat dealer I can't imagine you've been any less aggressive towards Jayco so can only imagine you've really not done yourself any favours.
So anyway after $105,000AU, nearly 5 years 2 motor homes, problems too numerous to list, being banned from the fiat dealer, given the run around buy the Jayco dealer, courts solicitors and god only knows what else, you feel the best way to put everything right is to provide you with another identical motor home
It begs the question, are you completely insane? After all this you've not learnt anything? Sue them for your $105,000 + losses and inconvenience and move on with your life buy a different van and start enjoying your self.
Why on earth do you want to continue to deal with these people, if I were them I would gladly take the van back and pay up just to get rid of you.
No normal person does something so significantly bad as to get them banned at a car dealership, over something so minor as a damaged grill!!?
Your argument of "merchantable quality" is diminished by the 20,000km on the clocks and 4 and a half years clearly you,be not been prevented from using it and when fiat tried to fix faults you went off the deep end, I can only assume you've done the same with Jayco.
In all honesty I think the best you can hope to gain is some of your money, maybe they will buy the van back at current market value, I can't see you'll gain much else, and starting a crusade against fiat because there van has a fault which they provide a solution for is going to see you in the grave long before it effects fiat's bottom line.
Because its a Jayco built van fiat's total liability is probably no more than $20k
All manufactures have problems when it comes to engineering something as complex as a van/car they learn lessons, make decision, change there plans and move on. That's probably something you should do.