The following may not be for the faint at heart, be forewarned.

For those of you in the rust belt, let me describe the horrible 
deaths that await the vehicles that bask in the portions of the world 
that are in what seems to be endless sunshine.

My recently purchased '80 Westi (for engine parts) had been left in 
the sun for an extended period of time by the dreaded PO.  Other bits 
and pieces of this story have been borrowed from dead parts from my 
Subaru, Ford Crewcab, and Squareback.

With the windows closed, the temperature reaches stifling 
temperatures, my guess easily above 120 degrees F.  The vinyl coated 
interior pieces stretch and shrink.  The vinyl stretches at a 
different rate than the wood it is glued to.  The vinyl cracks in 
hundreds of locations, leaving a shattered look to the walls.  
Gravity takes hold of the ceiling sections and pieces flop down to 
meet the upholstery.  Wind coming through the windows yank and tear 
at the loose vinyl.  Touching the vinyl on cool mornings leaves 
shredded portions of a once lovely interior in your hands.

Vinyl left directly in the sun turns black, cracks and falls away 
from it's own weight, leaving ghostly pieces behind, ready to fall at 
the slightest movement.  It looks like someone has been turned loose 
with a torch.

The upper bunk vinyl faces the ceiling and gravity hold doesn't take
here, but the additional temperature causes the vinyl to shrink 
together in folds and ripples, like waves near the shore.  The peaks 
of the waves reach the under side of the fibreglass top and wear away 
the velvet surface.

The velvety surface on the inside of the pop-top, which effectively 
eliminates condensation, has turned into a powder that silently 
falls away at the slightest touch, looking like interior snow.  
Fingers can create grafitti on the ceiling.

The canvas of the pop-top looks pristine and rarely used.  This 
appearance is deceiving.  As you unzip the window to gain some 
ventilation, ones gets permanent ventilation as the stitching is so 
brittle that instead of the zipper unfastening, the whole zipper 
falls away into your hand, leaving a torn opening behind.

The curtains dry up, shred, fall away to leave an almost 
powdery residue to mark it's presence.

Upholstery also dries, fades, turns to powder.

The plastic handle covers, and other dash pieces dry out, 
and leave a lighter whiter piece.  It scratches easily, and can't be 
brought back to it's once former appearance.

Exterior window rubber has also shrunk, pulling away from the metal 
and glass, allowing the occasional water to enter.

Chrome and plastic window trim has faded to black.

Tires dry out and crack.

Paint fades, reduces to a powder, blows and washes away to reveal 
colors and layers beneath that are supposed to be hidden.

All this damage comes over the vehicle slowly, more slowly than rust, 
less evident than metallic oxidation, but just as damaging to the 
respective parts.

All good reasons for car covers, garages, carports, etc.

- Jeff
'80 Westi, '67 Sqbk, '64 Ford Crewcab, '87 Subaru