I'd try at least once a day. One day he may suprise you. What about putting the carseat in the crib to get him use to being in there. I'd just keep trying and if he doesn't want, put him in the seat. A friend of mine has a 13 month old that still sleeps in her swing every night.

MY SON RYAN WHOSE NOW 10 MONTHS OLD MADE SLEEPING SO EASY FOR ME. BUT WHAT TRULY MADE MAJIC WAS WHEN MY HUSBAND BOUGHT ME MY ROCKING CHAIR. IT DID MIRACLES FOR ME. I THINK ONCE I SAT ON IT HE KNOCKED RIGHT OUT. MAYBE YOU SHOULD TRY GETTING A ROCKING CHAIR AND JUST SINGING TO HIM. I KNOW MY BABY GOES RIGHT TO BED. GOOD LUCK LET ME KNOW IF THIS WORKS!

you need to try your best when he naps putting him in the crib etc i did this with my daughter, i was reading a book a johnson and johnson book on sleep in infants and they said it is bad to let your child sleep in there carseat overnight because sometimes they slouch there head forward ya know and that can somehow cut off there breathing, i dunno how but i read it in that book but i am glad now my daughters in the crib, i let her play and lay in it throughout the day then layed her in it for naps then did the night thing and now she sleeps in it no problem!

keep trying . thats all you can do...babies are all about routine and what they are used to. I would let him cry it out for 10 minutes or so ..usually they fall asleep after a good cry.