After 10 years of abuse, I have the following rear bumper experience and
recommendations..

Buy the bumper rub strip "plugs" at your local dealer - you cannot get them
anywhere else. - for $1.50 each.  Keep 8-10 on hand.

Attach your bumper end caps (average life - 5 years) with carriage bolts
instead of using the clips. They tend to fall off and, at $40.00 apiece or
so, that gets expensive.

Remove end caps, rub strips and four bolts holding bumper (mine is diesel -
so watch the accumulated particulates).

Take large double jack, brace bumper on assorted (real -- presswood won't do)
logs and beat into shape again while thinking pleasant thoughts about
children (I have eight), ex-wives (two each), mother-in-laws (again, two
each) or coworkers (lots).

Remember, there is a natural curve in the bumper - it is not straight.

Reverse procedure to install.

I do this about every 18 months.

By the way, living in El Paso across the river from Mexico (and having worked
on both sides of the border), Mexico is a hot bed of VW's.  Of course, they
have the pre-Vanagon Station Wagon with a monstrous plastic radiator on the
front for their VW
"buses". Mexico never imported the Vanagon.

David in El Paso