I think in the future I would buy some offroad equipment for the P38. I had the same problem when looking for offroad stuff for the unmentionable jap.
For me the p38 would be great for greenlaning, but in order to stop leaving bits here and there I think my first buy would be some bumpers and guards for the under carriage etc. I have seen so many disco's, range rovers trailing bumpers behind them its unreal. Sometimes they could have been a little more careful mind you. I also have some concerns with the air suspension with regards to serious offroading. You never know whats under the mud sometimes, only takes a stick pointing in the right direction to rip of a height sensor (or damage it) or puncture an air bag. Correct me if I am wrong I bet they are dam tough but still my own worry (I have had to untangle them from normal springs in the past. So I might consider changing out the air bags for lifted springs.
And Tyres! forgot about that, perhaps my first buy. Rubbish tyres will leave you stuck on a wet grassy slope, MT's AT's its a balance. Best muds I ever had where Special tracks (nosiey as hell on the road, enough to send dogs reversing into hedges).
At the moment I keep the old unmentionable, for the laning, people laugh at it. But the wife bought it in 2001 and apart from the mods never had anything, (touch wood) apart from me modifying it, go wrong. Also never caught the bumpers front or back. It is however very uncomfortable and I would prefer the p38 with this in mind for laning in the future. This is one of the main flaws with it, and the p38 excells at keeping you comfortable for a days laning I bet. I would be the same in a defender, 6ft4, aint enough room in most motors to be comfortable.
I don't think I have ever had more than a trickle of water come through the door seals either. Use the right method described in many a wading guide. If you have no common sense your screwed before you start.
My P38 had been dunked at some point and i an still suffering the niggles, all the bearings on the ancillaries have now been changed. Had some rusty connection problems. Plus I reckon that it had been hydraulic'd during the process.