Go down thru the guard matey. Thats what I am about to do to my XH...and it is so simple to do. The only other advice I have for you is to perhaps make something of a box for the pod to sit in under the guard.
Come to think of it has anyone ever tried putting the standard box under the guard? Would be interesting to see if this works......will be checking this first me thinks

I very much doubt you need a second battery.

You should be good for at least 4000wrms off a single battery providing you have an adequate earth.

Wasting your time imho.

Worst case scenario, you're only having to run the cable connecting alternator to your secondary battery that is in your boot, your subs(I'm guessing you are doing this due to subs) will be right next to your new battery, reducing return cable. you'll have better weight balance(I know it'll only be a few killos, even still, better in the boot) And you still have an airbox! The pressure, and heat reduction have their advantages.

Don't get me wrong, you'll have SOME advantages to having the filter in direct airflow, be it in your wheel arch or over your extractors, but do the benifits REALLY outweigh the cons? Heat soak, and lowdown pressure will only reduce driveability.. If it is a purely Drag, or Circuit car, then by all means, keep the car above 2500RPM and you'll never notice, but even my driving style drops below 2500RPM on a regular basis. Can't be avoided on the street.. Damn traffic lights - Lets make roundabouts mandatory!

Until then, try and keep things functional to a point, if you're going to put a filter in direct flow, I recommend keeping it to a semi(not severly) restrictive point to help you with low down RPM. And if you're putting it over your exhaust manifold(or better, extractors) then do me the favour, and don't!

If you HAVE to remove your arbox and install 2 batteries into your engine bay, plumb(with great skill) your intake/s into the front bumper, around the radiator(infront) for maximum efficiency and capability.

Don't take this as gospel, just as an educated choice in opinion.. he he

Happy Motoring!