Alright, here's the gun mode. It's really simple, basically you just take his vehicle mode, separate the legs, pivot them down and then connect them back together. I also flipped back the wings to give it more of that 'space laser' look, plus it kind of evokes Rodimus Prime's rifle. For the legs/handle you can either leave the side leg panels up like in vehicle mode or down like in bot mode. I find having them down fits better in the hand, but up looks a little better:
(Sorry for the slightly blurry photos and ungroomed nails...)
Next up, manned space-cruiser mode! From vehicle mode, unpeg the arms and straighten them while still keeping them pegged to each other. Flip the main chest piece backwards to lie flat over top of the arms. Separate the legs, remove the cannon, flip it over and peg it back on using the tab on the silver barrel part and the slot on the back of his waist. Peg the legs back together. There you have it!
Here's how to do the rear (again, sorry for blurriness):
The whole thing:
Different, slightly closer angle:
Closeup of what inspired this mode, the 'cockpit', complete with seat!
That's it! Hope you guys like it.