Both
Materials for crafting are linked to every workstation, not just yours. So if, for example, you come across a weapons workstation in a barn on a farm and you use it to repair a weapon then the materials needed for the repair will be taken from your stash if you don't have enough in your inventory. I think it's the miscellaneous and junk categories.
Items are not linked. So if, for example, you were at that weapons workstation in a barn and realised that you wanted to mod a shotgun you'd put in your stash...you can't.
There are also functional copies of your stash box in numerous locations. It makes no sense, but we all just roll with it. Every train station and every red rocket station will have a working copy of your stash box in it, a magic portal to your stash. So you can retrieve an item to craft from any of those, which might be more convenient than returning to your camp for it.
reality is you are never far enough away from a stash box to warrant carrying more than 4 on you at a time.
didnt see any confirmation, if that didnt work, my username is steve5648.
what happened is TNT Dome #3 moves location at random. First time I found it (after the lengthy quest to get the key) it was way down the road nowhere near the other Domes. Then 2nd time I found it with someone else to let them into so they could get the T51b Nuka Cola Plans it was somewhere else again now with you it was near to TNT Dome 2 (with the Alien Blaster Ammo plans in). Looks like it randomises the location like it randomises the drops! There are 8 of those Domes hidden around there but right now you can only get into the 2 we went in (perhaps the other 6 will be the free DLC). Some are well hidden as well 
a long way from where you expect them to be 
