hmmm...not as easy to say as you would think. :)

The first 3 years it was exclusively outside. I then built a house with a 2
car garage and thought I would be able to garage it full time, but it didn't
turn out that way.  From December thru April, it still is exclusively
outside as it's spot in the garage is occupied by snow equipment, so it
takes a winter beating.  The rest of the year, it's outside all day and
garaged all night.  So I guess you could say that it's taken a relatively
good beating from the elements over it's life so far.  It's still in perfect
condition - No tears, frays, loose seams or the such.  Unless you live in a
bad area and are worried about vandals knifing it for fun or carry valuable
back there that you would worry about......although I've used mine on trips
all over with luggage, instruments and other things back there and I can say
that no one every bothered it even overnight at hotels and rest areas.

BTW, they used to sell an zippered end piece with mesh windows for it that
would snap on the back part and go around the lowered tailgate when it was
in the lifted position which would in essence, create a off-the-ground tent
out of the back of the truck....so you know it is watertight! :)

Good luck with whatever you choose...

IYM

I would suggest you look at the Extang fulltilt one. The hinged
slantside has several design flaws. The cover is hinged about an foot
behind the cab instead at the front of the bed like the Extang. The lock
at the back of the Slantside goes from side to side and hangs down far
enough to interfere with sliding cargo into the bed. The Extang has two
one on each side.

http://www.extang.com/docs/fulltilt.html