I camped with a couple friends that had DF Toy Haulers the really big 5er and one about the size of your rig. I'm disappointed that Northwood wouldn't be of more help.
If you were in Idaho, as your plate suggested I'd say contact Drakes RV Repair in Pendleton Oregon (541-278-8170), but from Alberta that probably isn't worth it. At the time I used them they had repair teams that had worked for all the manufacturers in the area including Northwood, Fleetwood and Keystone, they might be worth a call for advice/direction.
Here is an older
thread that might be helpful, talks about a spring manufacturer called Holmes Springs now called
IDC Spring
Two Wire Fox Terriers; Sarge & Sully
2007 Winnebago Sightseer 35J
2020 Jeep Gladiator Rubicon