The car is usually kept outside, but if the weather is really bad, I put it into our small lean to (open garage thingy), but this is so small that the back of the car still sticks out!
I bought mine from cover-zone.com the Monsoon cover. Very strong -well made, definitely waterproof. But it does need the two straps provided to go under the car to be done up - this means grovelling on the ground with a stick to push the straps through to the other side each time you fit it. Easy to undo them - the hassle is just when fitting the cover. Mine is only used in summer to keep my TR7 dry - for winter it's tucked away in the garage.
Good idea - but no - it tends to vary ! In any case - I would want the cover snug up to the base of the car (which the straps do) to prevent rain getting under.
I bought a cover on ebay (about 27 quid) and it was useless. When the car is out of the garage now I use a cover from Halfords, shiny silver colour soft inside, the small size fits well. I think it was called tyzek or something, but would recommend.