good point about the canvas cover, but vehicles weren't always on the front line, and lets face it, in a approaching sandstorm in the Western desert are you not going to give the order, "get the top up lads, we're in for it for the night" anyway, as you say, I'm making it open.I'm struggling to think of any museum I've been to where this has either been exhibited "closed up" or shown in historical photos alongside in such a state. In a frontline setting I'm guessing they went open top with all the toys onboard - and didn't even stow them and "hood up" when it rained heavily. I'd take a view that they'd cover the guns but otherwise keep it "ready for action" in bad weather - rigging the covers with a "quick-release" on the tie-down. Show it uncovered, show the interior detail - and show off your Goddammit modelling skills*!!"
Alternatively, build the more famous/well/known vehicle in this basic body shape and stick tracks under the arse-end!
* Not jealous, honest.