^ I use this site for my graphic design job for getting vector templates of various cars for vehicle wraps, decals, etc.
I just noticed that they have a section for tanks..... including WWII tanks.
These templates from my personal experience of using them, are generally scaled 1:20 and are usually accurate to within a couple of millimeters of possible error.
Please keep in mind that like istockphoto or shutterstock image web sites, this site requires money which converts to credits for purchasing a number of templates, so unless you want to do that, this site may not be for you. You can obtain larger resolution JPGs of the shown templates for free, but again, you might as well go for some of the other templates out there if you want to do that, as I believe they tweak the scale a little bit in those so people can't rely on them for accuracy. These higher resolution JPG's are not typically found on the template's page and there's a workaround needed (not illegal of course) However, any avid 3D modeler wanting to have an accurate design of their projects may want to check this site out. I know these templates (which come in AI, EPS, PDF, DWG, SVG, vector designs) have helped me a lot in the sign industry.
Professionally speaking, these templates are much more reliable and accurate for using in 3D modelling than referencing low resolution JPG photos or rough drawings and I believe they would help out anybody wanting to 3D model a tank or other WWII vehicle for RO2/RS, dev or hobbyist alike.
There is also a section for WWII planes, weapons, ships, etc.