I believe that copyrighted materials need to have a copyright on them to actually BE copyrighted, and no drawings or manuals I have seen from Vans carry any copyright. If I am wrong on this, I would like to know what page(s) somebody found copyright markings (I am working from 4 year old documents). Thus I don't believe that there are any legal issues here.
As to whether there might be some moral issue - well there might be and there might not. There is no way for anybody to scratch build an airplane using these plans, as there is just not enough information in the prints to build an airplane. Many critical dimensions are just not there, since you are buying piece parts from Vans with these dimensions built in. A set of scratch built plans for an RV would be 3 or 4 times larger than the current Vans set. So you're not really taking any business away from Vans with respect to physical hardware / kit parts.
You might be shorting Vans the $40 or whatever they charge for preview plans, but if you only share with people who clearly are already building (and thus have already bought the preview plans, as they are a prerequisite to ordering any part of a kit) then I don't think this is an issue either.
I have tried to convince Vans to sell their plans and manuals in digital, searchable format, but they are not interested. Since they also do not copyright these materials, I think the door is open to sharing among builders. Searchable plans & manual are absolutely essential for efficient building, IMHO!