Try a grand theft battlemech campaign. Z characters cross border to steal prototype weapons from X company, X Company has a small research station at Y planet, they are testing mechs, vees, asfs, and depending on era BA, a mix of things, but dependent on the company you are raiding see sarna.net for manufacturers, planets and equipment, and the books they are contained in, for more detail. Your goal break in an steal them, break out. Who you guys are and whose defending the outpost is up to you, but sneaking in is a little more interesting then shooting your way in, but by all means make them shoot their way out. Have different tasks, like stopping pilots from getting to machines, deactivating security systems, destroying C&C, and finally stealing the mechs and escaping well hopefully most of you will be escaping. I would not recommend making your characters attack battle armor or elementals, on the first go. Nor would I recommend any mission beyond 3025, fewer weapons, equipment, make for less book keeping, I am not a fan a minutiaing people to death the first time out, Battletech has more history and source material of just about any game out there so the choices are limitless.