Defense laser question.

I just built 3 defense lasers and played a nasty 12,000 point apocalypse game on Sunday. I wanted to stuff them with my imperial guard heavy weapon teams but my opponent ( my buddy Val) wasn't sure I could place them there as they are classified as a super heavy vehicle. So, my question is, can units move on top of friendly vehicles?
The defense lasers measured about 9 inches by 9 inches and stood about 10 inches high. There is a platform I built specifically to house about a squad of guard.
My other question is if I can incorporate the guard defense structures ( the strategic asset that gives a 3+ cover save) into these wonderful defense lasers?

If anyone has any advise, it would be much appreciated.