I posted this in the weldless thread. I have been designing one using strut for a while and found this site which has stainless strut and fittings.
http://www.strutchannelfittings.com/ They also have standard fittings. Their prices on fittings seem decent but they cost of their strut is...
I've had been designing a system using channel strut and found the fittings here.
http://www.strutchannelfittings.com/
I have not bought any yet but them seem to have a great assortment.
Also, if you want to design via CAD you can download the CAD files from Cooper which makes a brand of...
Try this
http://www.instrumart.com/products/18082/king-instrument-7200-series-rotameter
There are a bunch of options like flow rate, fitting material, and type of seals.
I used loc-line for the returns on my reef tank, but hadn't thought of using it like this. You can usually find it at aquarium stores if you need to pick up a few parts. The MashTube is a good price (especially the weldless kit). You can also get parts online for cheaper than McMaster at...
I'm looking at getting one each of the 10 gallon pots:
2 horizontal couplers with http://www.bargainfittings.com/index.php?route=product/product&path=46&product_id=83 for HLT
2 vertical couplers for MLT
1 coupler for BK
Sound about right?