(Since this is guess-the-cause I thought I'd post to the list to see
if this inspired somone else to figure it out... :) )

	1) Noise changes with vehicle speed
	2) taking off the rear wheel and playing with the drum and
axle makes it go away
	3) It stays away for 1000 miles
	4) A really hard brake application makes it come back.

	Can you get the klunk by jacking up one side and turning
the wheel by hand? That will fix which side its on for sure. Check 
both sides as long as you're back there- it could be coming
from the *other* side...

	Sounds to me like the klunk is a product of the rear brakes
(drums, yes?). Whether drum or disc, the rear wheel bolts/studs pass
through the brake part and then the wheel. Taking off the wheel might
allow a subtle change in the centering of the drum/disc, which then
stays noise-free until hard braking restores the noisy relationship.

	Drum brake shoes float to a variety of positions when not
being operated- I'd guess that Sami's camper does have drums, one
is slightly off-center or out of round, and something in the floating
part of the brakes is making the noise when it touches the drum.

	Easy check-see: Take off the drum and inspect it's inner surface,
then look for something bright and shiny that isn't brake shoe but has
been touching the drum.

	If its disc brakes, similar issues can happen with warped rotors-
a hard braking may change the rest-position of the caliper, which, like
the shoes in a drum, actually floats. The warped rotor could be bonking
into something other than brake pad...

	The other obvious possibility is a really bad pitting in a CV
joint, but braking wouldn't stress it and rearange it, so I consider
that less likely.

	Good luck, Sami