I am building a Mash Tun this weekend and I saw somewhere that people coil some stainless wire and stick it in the stainless braid to keep it from getting flattened by the grain. I have a foot or so of copper wire - will this work? Not sure how it will react with water. Any thoughts?

Go for it. Nothing wrong with copper that I know of. Many mashtuns are made of it.

The pipe for my keggle drain is copper, never had any off-flavors or anything...

I really don't think you need it in the braid if it is a good braid it will not flatten I have used mine in close to 20 batches and it has held up to 14lbs of grain on it (mine is a 5 gallon cylindrical igloo, so all the weight sits right in top..)

I brew on a system at the LHBS from time to time... I fricken hate the braid used on that system... The braid sucks IMO.

Get a nice false bottom and never look back.

Yep. there's definitely a lot of different types. The one I got from a water hose at depot really sucked. It flattened out like a snake skin.

Then a fellow homebrewer game me a piece of his. Not sure where he got it- work, I think. You could stand on it and it wouldn't give much.

I got my braid at Lowe's, so I'm thinking I'll add the wire to reinforce it a bit. I'm not ready to drop big bucks on a false bottom set-up just yet. So far this MLT is coming in at 60 bucks for everything. Been doing extract for quite a while, but this will be my first all-grain coming up. Next weekend I hope. This weekend I'm building the MLT and harvesting my homegrown hops. (CT)

I don't use any wire, but I am using 1/2" heavy duty braid. It gets mashed and stretched sometimes, but I squeeze it back together and straighten it after several uses.