Waterproof Heavy Duty Seat Covers

Has anyone used these universal seat covers, that are all over ebay, but strike me as a bit too cheap?  Are they actually waterproof? or just water resistant? 

http://www.ebay.co.uk/itm/201451218215?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Or these higher priced, but look exactly like the cheap ones?

http://www.ebay.co.uk/itm/FORD-FOCUS-2005-2011-BLACK-REAR-WATERPROOF-SEAT-COVERS/251488859906?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D35391%26meid%3Dd0e972e4c1db4adc8dd3a9a9e86b2340%26pid%3D100005%26rk%3D3%26rkt%3D5%26sd%3D201451218215

Unlike everyone else with an estate, I use mine 'back to front", so to speak.

The cargo is on the back seat and the Brandy the dog has the cargo area for her crate and dog things.  The cargo is actually placed on a sheet of OSB that I've trimmed to cover the whole of the rear squabs. At the moment, the seat backs themselves aren't protected by anything.

It's a rare thing, when I have rear seat passengers. The OSB is easily lifted out, on such occasions, ideally any covers would need to as easily removed too.  I'm guessing universal ones are easier to get out than the tailored ones.

I'm approaching that time of year, when I need to collect things from the nursery, like young plants in moist to soggy compost, numerous bags of horse manure, dressings and composts etc.  I don't particularly want to make my Mk2 Focus rear seat wet.  It didn't matter so much when I used the Astra. 

I could also do with a rear seat cover for the Mk1 Focus but with seat belt holes, for Brandy's harness to seat belt socket retainer.  She seems to find the muddiest puddle to walk through before getting in the Mk1 Paw prints galore decorate it not to mention spare fur everywhere!  It's really awkward to get her crate in the Mk1 as it's a hatchback, it can be done, but it's awkward and not worth it for short journeys..