^^^ what he said.
The Td5 is no more complex than a 3.9 EFI V8. yes, there is an ECU (it sits under the RH seat along with a fuse box), they can be made watertight (using an IP65 box and lots of sealant) or just get an ECU extension loom, plug it in and stuff the brains up in the roof or at least bulkhead height)
but just "average" river crossings, hood deep where you get a few inches of water in the footwell and a nice bow wave, are no problems at all, no worse than any other diesel engine (i know, i've done them in mine!)
The 300Tdi is a good engine, don't get me wrong (i've had 3 of them) and now on my 2nd Td5, but they're night & day in comparison.
weak point of the Tdi is the cam belt and overheating issues (although carry a spare cambelt, 8 push rods and maybe a couple of rockers,one hours work your back on the road again)
weak point of the Td5.. early ones (up to about 2000) had a weak cylinder head and could
cause fuel to leak into the oil sump. later heads were redesigned with only one fuel drilling.
the in-tank fuel pump can die too, but dropping the tank (or even cutting a flap in the rear load bed floor) to facilitate a quick change is no hassle (i've got the dimensions here of where to cut if you need them)
The Td5 has lots of sensors, yes, but only the crank position sensor (screwed onto the bellhousing) can cause engine STOP, the rest of them will just revert the ECU to a factory mid way setting, so no hassle.
the sensor is about £30,no big deal.
The nanocom is an excellent piece of kit. you can do all the settings that the dealership can, and more, like uploading different fuel maps (if you have them) for more power etc. you can set the alarm states, or disable the alarm etc. you WILL need the nanocom if you change an injector, as they have individual codes on them (the engine WILL run with the wrong codes in, just not as well as it could, so worst case you can get yerself home)
Td5 is highly tunable... mine is currently 170bhp, Ian @ IRB developments
has managed so far to get 208bhp with a VNT turbo from a Td5
and still keep within UK emmision rules, pretty impressive.