The reason they want you to get it weighed is so they can charge weight fees as part of the registration requirement for commercial plates. On a large vehicle these fees can be substantial. They don't care if it's not used for commercial purposes it's still a commercial vehicle. The only way I know to avoid these fees is to register it as a camping vehicle but it must have a "permanently attached camper or shell". I guess you could install an old shell and remove it after the registration process. A camper does not require a weight cert.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine