Andy,
If you want to wash out any accrued mud, silt and what have you, it really needs to be dried out quite well afterwards, not sure what facilities you have there, but I find a hot-air gun, on low setting is handy (careful of any hsoes running through rear cross-member), partic befoe painting or injecting sections with your fav stuff.
After wading in anything but clear water, I expect some of your cross members might have silted up a bit, as Thomas found here:
http://www.BusGoofs.com/forum/viewtopic.php?t=312
You can get into either end of this beam just under the rear trailing arm pivots and wash or rake stuff out, but hoses and some wires may run through this both sides. There are bungs accessed from the rear of this member, two each side normally, quite large. I'd have a lickle rake around from the side with a bit of fencing wire bent over at the end into a 1" 'U' - never trapped one irrecoverably yet! You might be surprised you're still raking stuff out an hour later
Then the two fronts, the rounded rectangular bash plate support beam and the big round sub-frame tube behind it, though they are thick and shouldn't usually corrod badly, but worth a look, partic if you want to always be able to get the rear bash-plate screws out!
Then the sills, as Cate says, have two plugs on their outer faces below the pillars, small round ones, at least two of those oval ones in the floor going down into the sill, amazing what you find down there, but can be difficult to get back in.
Large round ones on the inside faces of the sills underneath, at least two and then the really useful ones, 3 (on a Doka) different ones each side facing forward just above the radius arm pivot inside the wheel arch. These are good for raking the different box sections above the sill as well as the sill itself, or washing through.
The rear chassis longerons usually have an assortment on the inside faces, and one on the outside and a natural drain hole where it changes section and drops down to the rear cross member. And with the bumper and tow-bar removed, a 3' 6" fencing wire poker can achieve a lot from a rear entry
I prefer to dry scrape and vacuum (using a hose about the size of the brake vacuum hose to get right in there, angle off the open end else rust flakes soon block it off, need v. powerful wet/dry drum vacuum) before a paint or wax treatment, but this is not a 5 minute job on any of the sections
Whether you scrape/vacuum or hose them out once a year, it'll probbaly save a full sill or welding job after staying wet with mud for 4 or 5 years from what I've seen.. look what Thomas had to deal with. Until you run a flat scraper along a major section, removing underseal and paint you have no idea whether the thing has any real integrity left...
Sending you the odd piccy,a s I can't find the link to old ezboard pics..
