I don't have many Terminators done yet.
I do have them all built but only two painted so far. He took about 5 hours to do with all the coats of white to make it smooth and consistent.
Here's a look at my Apothecary Terminator. I used the Chaos Autocannon with Assault Cannon barrels attached to the end. Looks close enough to the Imperial one. I had to file off the "Chaos" looking things to make in convincing.
The Apothecary arm is mounted on a regular Terminator arm that was cut just below the elbow. Some filing and cutting away from each piece and they fit close enough.
I'll see if I can get a pic of my recent Attack bike in the next couple days to post.
Link: Follow my White Scars Doublewing project
Since this post is quite old now... I've been able to refine my "white" and have a much quicker process for painting models white.
The new technique is here.