In Battletech..with enough thrust...
..even a fully loaded Cement Truck can fly.
Art really doesn't apply, which makes things interesting for people want UNIQUE looking vehicles, mechs etc.
Getting things to fly isn’t particularly hard with enough thrust. Getting them to fly efficiently is an entirely different story. Getting them to do things like.. turning safely is also harder. The best description I’ve heard for steering something like a flying dump truck is like trying to turn a supersonic ocean liner.
With a sufficiently efficient rocket, you can make a dumpster fly. You can even get it to fly straight with a stabilizer. The drag will be through the roof though