Rob T, personally I take the wheels off and brush off the underside whilst dry
You can then use this opportunity to check over all the bits that should be tight, plus the brakes, check for any hoses/cables chafing & I then mask over the brake discs and give the under-arches a blast over with a coat of Waxoil, or similar
Agree, best done dry using a brush
Water to the underside, chassis washers and Morgans don’t work too well together
Too many nooks and crannies
I’d use Tectyl 506 spray after you’ve cleaned as it’s transparent amber coloured so you can see the condition of everything
Much nicer than black stuff everywhere
Just be aware that the overspray gets everywhere so do it outside on a still day
I did it in my garage and then realised very quickly I had to sheet everything including me - my Mog, me and garage ended up looking like the end scene from ET
