I am late to the game here - but I wanted to post that according to a LOT of car seat companies, the BundleMe or products similiar to the bundle me that go between baby and car seat are not saftey tested with the seat, void all warranties and are considered a saftey hazzard.
As far as bunting is concerned the only way to be sure your bunting is considered safe for a car seat is to put baby in bunting, strap baby in car seat, tighten straps as usual. Then, remove baby from car seat (DO NOT loosen the straps to do so!) take bunting off baby, put baby back in car seat and check to see if the straps are within the acceptable tightness of less than two fingers between baby and strap.
This sort of cover, the 'shower-cap style' is the only reccommended car seat add-on as it does not compromise the straps of the infant seat or the way the infant is secured in the seat:http://www.amazon.com/Faux-Shearling.../dp/B000284WX6
On the up side, I think they are as cheap as $9.99/$19.99.
This is what we're using (but the land's end one) along with a blanket if it is really chilly and a weather appropriate outfit.
I know it may seem sort of silly, but after researching car seats and having it installed properly by the car seat tech I would hate to compromise saftey on something a silly as a cover!