The covers have a hinged lid but I have removed them for both times I incorporated the shapes into a model. I first used 5 covers in the "Tortoise", a 1/35 mech I did two years ago:
Four for the thruster units, and the other was made to be a missle pod. Although it is some kind of vinyl I believe, a little sanding to remove the gloss and I have no trouble glueing or painting them with standard off the shelf products. There is also a small hole at the narrow end, I guess for ventilation... More recently I used 6 more on the Gibraltar:
A little difficult to see under all the other greeblies and nurnies! They made nice modules and again I had no trouble in glueing them to other materials. I have future plans to use them as cargo pods in larger numbers on ships or maybe railroad cars. To look at them as pictured above, you could easily ad a handle, two little wheels, and a city logo. Now you have a garbage or recycling cart! Always look beyond the items intended purpose!