ArtMetal

Stephen Fitz-Gerald
I agree with hjnwt,weep holes are a must...
In addition I make sure whatever goes in the ground is solid metal ,NOT tubing. When I make a rail with 1 inch square tubing posts,I weld 8 or so inches of 3/4 round bar to the bottom of the tube with at least 8 inches up inside the tube as well. This is a good stiffener and means you get a solid bar in the ground.
Also I personally don't do any installs. I tell the client upfront that he must make a separate contract with a good contractor ,and then I recommend him mine.Ninety percent of the time they take my advice. I've been working with a fantastic and reasonable contractor doing my installations for 20 years.He has the PORTABLE TOOLS, the LIABILITY INSURANCE, and the CONTRACTORS LICENSE,none of which I have. I am always present for the install and WORK FOR FREE on that day,but shoulder none of the official responsibility.This arrangement has served me well over the years.
Bidding a job is often a sticky wicket.My technique is thus;
Since I DESIGN as well as FABRICATE,and nearly everything I make is site specific,I have a base price(or minimum) of $275 per lineal foot for the simplest of designs. Obviously curves or stairways are more difficult to execute so those are an added charge.My most expensive is about $500 per lineal foot (Art Nouveau stuff):
http://www.sfitzgeraldfineart.com/custom-gates/
(page two-The Guimard Gate)
Your question about warpage has two solutions;
First you clamp the shit out of everything you weld ON YOUR FLAT THICK JIG TABLE,especially if it has uneven spacing of the welds.Clamps are cheap,there is no such thing as "over clamping". Also I have consistently gone to thicker and thicker railing members over the years,cap rails,newels etc. to avoid heat warpage from welding.It's just easier and there's less chance it'll go haywire on you if it's thick and heavy material. This is of course even more true of stainless and other non ferrous metals...
I hope these logistics help.
But we're all different and have different strengths and weaknesses. These contrivances help me but that doesn't mean they would work for you. So take from this advice what fits and is helpful and discard the rest...In the end you want to feature your strengths and sublimate your weaknesses. How you do that is a personal thing...