I waxoyled the chassis of my 90 few weeks ago.
It took 2 weekends to clean it properly (I mean "properly
with pressure washer,water and gasoline as last.
Once dried I applied the Waxoyl.
Actually (some weeks later),the chassis still look like new (ok,no offroad trips recently).
What worries me a bit is that the film is sticky still.
A friend of mine in UK said it gets really tricky to clean the chassis again after a mudbath.
I hope it'll dry out sooner or later,but I have the feeling it won't happen!
As for the undercoating:a proper Waxoyl undercoating is available,but
I know a lot of people who use Waxoyl for regular undercoating...as the label suggests.
I let the inside of the chassis untouched,as I plan to get a couple of Dinitrol can,
which should be a helluva easier to spray inside.
Whaxoyl is an absolute mess to spray in correctly as it drips everywhere (read:on yourself and the driveway) and you can never know how you did the job.
(talking of myself)
Anyway looks great and it's better than a KITA.