how thick should shroud be?
 

It's for a panaflo m1a on a heatercore. My shroud is built into my case, and I'm guessing the fan is only 1/2" from the heater core the way I have it rigged. It's pretty noisy, even rheo-volted down to 9v, and the airflow isn't great.
Would it be worth the case hack work to increase to 1"?

I don't understand why it's noisy. Is it a rattling noise, or is it the fan? If nothing else, try just replacing the fan.

Truly, only you can determine if it's worth the case mod. However, if you post pics of your current setup, we can suggest alternatives or possible case mods to allow a deeper shroud.

Panaflo M1As aren't quiet by any stretch of the imagination. Try unbolting the fan and suspend it in the case while it's running. If the noise is about the same, then that's just how loud the fan is. If the noise is due to rattles and vibration though then it will be a lot quieter. I use 1.5 to 2" for all my shrouds; less and you put a pretty serious restriction on the fan's intake side (for fans pulling air through the heatercore).

All my shrouds are 1.5" deep
 

You can build a new one from sheet aluminum in an afternoon, a day at most. That will support anything short of a metal fan. I always use a draw flow for mine so I don't know how much improvement happens w a blowing system, but not real noisy. (Looks over at box and sees temp of 79.3 F for CPU) :D

There was a thread about this on Overclockers Austriala IIRC. Basically up to 6 inches thick or so is ideal, but an inch or two is pretty good for practical reasons.

To gain another 1/2inch it'd be wasteful IMO, unless it'd be a very quick, easy mod. Just run the fan at +5volt, or +7volt (use the +5v as an 'earth' for the fan while running off of the +12volt rail). It's better to have the fan sucking IMO when used on a rad...

DO read this article:

http://www.nmbtc.com/pdf/forum/engineering_101.pdf

Page3 has the relevant info to this particular discussion, but the whole paper is useful.

Excellent article. I did a little impromtu modding and got the fan almost 2" from the rad. Quieter, better airflow and cooler water.

My over-engineered radiator duct will have the pusher fan 1 inch away, and the puller fan 2 inches away.

Good New: Danger Den has some pre-made shrouds for sale.
Bad News: The Shrouds are for 120mm fans and They are only 3/4" thick.

I may have to buy 3 to get out to 2.25" thick.

Order Shroud Separately $13.95 each