I think you pretty much nailed it, Geoff.

I can see where a pad under certain types of carseats could work its way out and the seat is no longer as tight as it was...that sort of thing.

But the bottom line is that the carseats, etc., were designed and tested without any accessories and adding any could (not would) cause the carseats to perform differently than designed and tested. Sort of like the warning on bicycle helmets not to put any stickers and/or paint on them.

In the case of a serious accident, the use of accessories could be of danger -- and certainly void any possible law suits against the seat manufacturer...and with insurance companies so tight with their money, might even cause some problems getting medical bills for injured kid(s) covered...even if the seats did not "fail".

Use at one's own risk.

I have a boy who has been asking why we did not get leather seats (he has expensive tastes for a 12 year old!) -- I just tell him that no way would I expect leather seats to stand up to 3 growing boys...they are not in car seats for all that long!

Vaughn and the ABC Boys
Alex, Bryce, & Calder
3-31-97 @ 28.5 weeks
http://s515.photobucket.com/albums/t356/vaughn3abc/