There was a Crossley Truck in RAF livery in the Models of Yesteryear range. Nice piece, that one.
I´d say WW1 is difficult to find, somehow; there are quite a number of plastic figure accessories for WW2 and Modern, though, some of which might be adapted.
Fiddler's Green offer
a tent hangar in 1/60th scale, although that could possibly built as easily from scratch, I guess (especially if you need one large enough for a DH10.

); I got some of their aircraft plans and their Lanchester, and they are nice and fit together well.
I´ll look through my links to see if I can find some more stuff.