This is hard to explain so please bear with me.
As I understand it pretty much the following only have been tried:
Cold air intakes (various).
Gasser (petrol) engine from '02 '03 models.
Add-on snorkel with a small degree of ram effect but mainly for cooler more dense air.....more for keeping the intake out of rivers in my view and bulldust in my country.

Question is are there any other alternatives...has anyone made an air box that provides greater filter area and less resistance to the air intake pathway?

For obvious reasons I don't want to sacrifice filtering efficiency.
Would like to improve it.
We can gain with exhaust mods that will help the GDE tune do its job. It will come to mine in time but I want to build this into something TRUCKLIKE starting now but over time.
Why am I stuck on filters?
I believe the internal engine environment is critical to the longevity of any engine. There are people who would argue that regular maintenance is adequate to specs - I want to see if I can tick the long LONG distance running box.

SOON I'll achieve a clean internal environment when I've installed all of the following:
a Fuel filtration: water separating filter @ 2 micron.
b OIL by-pass filtration: additional benefits of this mean I can install Oil temperature and pressure sensors in the transition ring for the By-pass filter tap-off.
c COOLANT by-pass filtration: water temperature will be measured in real numbers with my installation.
d Cyclonic Oil Mist catch can that is better sized for the 2.8 CRD at only 3 inch max diameter and body 4 inches high but with the same basic features as that Mann and Hummel many have used and 3/4 inch Hoses with a washable separation filter medium.
Future:
e Power steering line filter
f Transmission oil by-pass filter with Pressure (line) and temperature gauges.

After much pondering about how to gain space under the bonnet (hood) I finally have got myself well underway. This week I should be up to installing a new battery tray that will lower the battery (also tilting it slightly into the engine bay) and turn it longways through 90 degrees.

It gains a huge amount of room (relatively) and that under hood junction box will be easier to open not requiring that silly waste of space for tilting with a new removable hinge pin.
Another unexpected gain:
Adding more substantive battery post to cable connectors - which are mathematically out of balance in the KJ. Stock arrangement could cause the astable electrical situations whereby these things stop running out of the blue (deserves its own thread).

So if the air flows out better should it not take air in better?

Achieving better breathing:
I won't use a cold air intake.
For the VM 2.8 CRD:
Has anyone ever built a tailored air box that has a larger filter area akin to the hotter tuned motors of similar displacements for example Highly efficient cylindrical in Toyota, Ford Ranger styles OR
Even the new Colorado here makes 550 Nm or something like that - I want to look at the air filter for one of them.

Perhaps the G2 series of higher efficiency filtration media offered by Donaldson just as an example, offer a course of action.

I can see how I may be able to double the filter area using 2 of our stock filters and fabricating a better, free flowing airbox.
complex but deserving of an explanation. Even a 1/2 size element in addition to a stock unit of ours would be a gain.
My 3D thinking brain sees one in place.
It may be too hard but I am sure I can truly see ways of doing this.

That is where it is currently - I expect the detractors but I have my reasons for dabbling so. I am happy to disclose these.

Any leg-up that could be given would be appreciated.
I have had no joy with searches.
Cheers

What if you used a sealed airbox in the engine compartment, with a snorkel going up to a pre-cleaner on top of the roof. All of our heavy equipment have them and some have original air filters from 10-15 years ago. About 12,000 hours worth.

That's where the best quality of air will be and is out of the way of the water.

_________________
05 Liberty Limited CRD, converted to KPA 2863 ball bearing and billet turbo, 50hp injectorsl, complete egr delete, cooling fan delete, weeks intake kit, cummins in tank lift pump, ARP studs, 3" turbo back exhaust, samcos, etecno plugs, GDE trans tune, custom GDE engine tune.

Cheers.
That's clearly the starting point but sadly not the whole answer.
A snorkel is certainly on my to do list and indeed that's part of the standard installation.
Off road here necessitates a snorkel only a foo would go very without it.

I hoped for some ideas on increasing actual filter area from others.
Not aware of an air box being remodelled but there are some clever blokes here so I thought I'd ask.

Seems I might have to start from scratch - fluid dynamics is one of my areas (a lot of training and experience through a long working life).
A simple manometer picks up the differences through this system from friction losses easily.
They are surprisingly high.