Search:

Close to the shooters I would consider concrete or asphalt so that the brass can be swept up provided it is not in the cone of fire.

Further out and keeping in mind that you don't want to track it...

There are plenty of ways to skin a cat - if the trenches have sloping bottoms towards the downhill, are say 200mm+wide and filled with bigger stones eg AP40/70 (like in concrete retaining walls) on...

You only really need Novaflo (with a sock) in clayey areas where the clay will gum up a trench. If your trench is pea metal or loose stones and more than say 200mm wide it should be ok but talk to...

Drainage

If ground is flat naturally then you guys in the South don't need a North Islander to tell you what liquiefaction is.
If ground has a slope then it's a good idea to do slit trenches say...

Re indoor building vs fumes - if you want a building with common access to 100 and 200 ranges I would recommend on building with two doors to the outside which holds two ranges
Exterior style...