...and Beamish have a smaller Thresh disinfector: http://beamishtransportonline.co.uk/transport-stocklist/horse-drawn/1904-patent-thresh-disinfector-ref-1970-61/
The disinfectors were normally size QQ "Quest" disinfectors supplied by The Thresh Disinfector Co, 4 Central Buildings, Westminster, SW London and mounted on Foden chassis. I'm not familiar with mobile laundries - any photos?
Howard, I don't know if you've seen this or indeed if it's of help (click on the photo to enlarge): http://wheelsandtracks.blogspot.co.uk/2011/11/c30-cab11-uk.html
Also, you may like this snap from my collection - sadly I can't read the WD numbers (they possibly start L4....).
This was mentioned the other day: http://www.ebay.co.uk/itm/living-van-shepherds-hut-steam-Vintage-truck-or-vintage-tractor-van-/151632261205?pt=LH_DefaultDomain_3&hash=item234dfcb055&clk_rvr_id=807325954612&rmvSB=true
Here's a Bedford QL "type 2100" - which would make it a passenger coach according to Robertson. So it's probably a QLT 'trooper'.
http://elinorflorence.com/blog/118060
As the plate says, it's a 10cwt mortar trailer!
It dates from WW2 and looks very original - though the tow hitch should be on top of the frame rather than underneath.
FT - wow! If only we'd made contact 20 years ago the fate of JUV833 may have been very different.
For interest, here are some pictures of JUV825 from the film I was thinking of - "Out of the Clouds" (1955) - said to be Heathrow. Apologies for the quality! I wonder if there was a similar Humber at each of Britain's main airports.
Contact the RLC Museum and see if they have the card for 38RU76. That may give you the wartime serial number it was converted from.
http://www.rlcmuseum.co.uk/docs/accessarchives.html
Was the entry fee dropped 18 years ago? My memory is a little fuzzy but I expect it was dropped, along with most other national museums, when the VAT refund scheme was introduced. For the IWM this applied from 1 Dec 2001 - see SI 2001/2879: http://www.legislation.gov.uk/uksi/2001/2879/contents/made
Vanguard are well know for having an eye catching installation - it's normally a Hawker Hunter. This replica has been up since the start of the WW1 commemorations. More here: https://mobile.twitter.com/VanguardStorage
There's a fair amount of information on these interesting machines in Wheels & Tracks #41 and around the web, not to mention here: http://hmvf.co.uk/forumvb/showthread.php?16812
There's also a bit of footage here: http://www.britishpathe.com/video/indian-l-r-d-g-unit-1943