2004 mitsubishi outander rear wheels tilting - extreme tyre wear.

Get this looked at as soon as you can, ignoring it will cause extra wear on other parts pushing the cost of repairs from 'Ouch' to 'Aaaarrrgh!'.
The thump may not be the brakes. Does it thump as bad if you do it in reverse? As the vehicle brakes it's entire weight shifts forward so the most likely cause will be something worn out on the suspension, usually parts like a worn rubber bushing, worn shock absorbers (dampers), or a broken spring. Get all four corners of the suspension checked over as sounds can travel and appear to be coming from a different area of the car.
As to the camber. It should have a tiny amount of negative camber as this helps prevent 'Wheel Tuck'. This is where the wheel and tyre tilts or folds under the vehicle during hard cornering. Tucking can 'pop' the tyre off the rim risking the vehicle tipping sideways and rolling over.

take the car to a suspension specialist shop and have the rear wheels aligned first
have the suspension checked for worn mounts or bad springs
it is very important that the rear end is aligned before the front end
suspect that the suspension rubbers need replacing as it is over 6 years old
the tyre rotation is a myth perpetrated on drivers to sell tyres
when the tyre construction was cross-ply and not radials yes rotation then on cross-ply tyres could get the wear to even out but with radials once the wear is started then the tyre continually wears in that pattern regardless of which wheel it is on
even if you take that tyre of the car and put it on a trailer , it will still continue to wear in that pattern
tyres are no longer rotated but simply put front to back on the same side other wise the belts flex in a new direction in the tread and fail earlier that expected
besides that fact that tyre rotation will not allow you to monitor for suspension problems or wheel alignment problems and cost you 4 tyres at a time instead of two

You may need a Camber kit installed, the camber is preset on most cars these days but they do make kits to add or subtract Camber, you likely have a Camber issue here. Camber is the tilt of the wheel outward or inward, to much positive can scrub the tire like you stated it was doing. You need to find a really good front end tech and explain the problem to him and he can custom align to stop the wear issue.

Your car needs a Rear Wheel Alignment, the components need to be inspected/checked for wear and then aligned. Worn ball joints, wheel bearings and so forth can cause bad alignment & tire wear.
Also it's hard to get an accurate alignment once a tire is worn on the inside or outside of the tread.

Car Tyres will eventually wear out!
I will assume that your Tyres are wearing out quickly and unevenly on one side of one tyres: this is a 'typical' scenario (with some symptoms being vibrating steering wheel, car pulling on one side when braking) when I highly recommend a full wheel alignments as well as getting your Tyres dynamically balanced: a good autoshop or Tyre shop will confirm the issue.
Another possibilty but not as common is your car braking system could be defective thus causing one or more wheels to lockup before the other thus causing tyre burns and wears.
I suggest you consut a mechanic! Hope the information is of some help and let me know how you go!

Had a similar problem with a different car. Rear struts / spings were worn. Caused rear to sag enough to push wheels out and wear out inside portion of tires.

It's probably caused by a ride height problem, most likely related to worn springs. It seems unusual in a six year old car but I've seen it before. Go to a shop that does 4 wheel alignment and make sure to get the print out from the alignment machine. A good alignment starts with ride height measure, and rear wheels are adjusted first. When you read the printout, make sure something has been done to the rear. A lot of techs only adjust the front

Tyres not wearing evenly in extreme cases

A noise like a locomotive running on rails , sort of a low rumble combined with a whine.

Normally they make that noise in a straight line and get quiet when you turn the wheel as the loading on the bearing then changes

As they are driven by a drive shaft it is impossible to test them by spinning the wheel with the car jacked up

When this happens it means that you have a convergence problem. Go to a tyre fitter, mention the problem, and after fitting the tyre ask to perform a balancing and convergence setup on rear wheels, this should fix the problem.