Barry,
I have an 8 inch and 12 inch version of that scope. The 6 inch should be a lot of fun.
Here are some images from the 8 inch version.
If you are having trouble with the collimation / locking screws then stronger springs might be a good idea. If you put in 6 springs (instead of 3) you might not even need to use the locking screws, they just stop the springs popping out.
Collimation and focus is going to be critical. If it's off, the images will look terrible. I'm of the view a full secondary offset is best - i.e. both away from the focuser and towards the primary.
I have a tip that has helped me and might be of some use: cut 4 wooden blocks that fit exactly between the secondary mirror and the tube wall. One for the top, bottom, left and right. This will do 2 things:
1) it will help you make sure the secondary is in the exact center of the tube (left / right) The left/right secondary collimation screws tend to swing the secondary mirror through an arc and will move the secondary mirror away from the center of the tube. Only use those 2 screws to get the secondary into the center of the tube. That will also place it directly under the focuser. Rotate the secondary to align it with the primary and use the remaining secondary screw to get the tilt correct.
2) it's a great way to check the offset is correct. The top block should be 2 x the offset longer than the bottom block.
There are lots of good resources out there, such as
http://www.catseyecollimation.com/mccluney.html
My advice is to take your time, and don't skip any steps. I have seen scopes where the factory installed center spot was off and also where the focuser was not square to the tube. You would think this could not happen, but it does.
Once you are done, rotate the tube and see if the collimation holds - if not investigate why.
The catseye tools are a good investment - the "radiation" center spot is awesome when paired with the INFINITY XLP and it's real eye opener to see low little movement is required to loose colimation. In reality the Teletube XL is probably all you need. A laser won't help much sorry to say. A final tiny tweak of the primary under the stars with CCDInspector can help you get the last little bit. You will also need to find a way to get perfect focus - for me it's a robofocus and FocusMax.
Happy imaging.
James