Yo dude
I think some it may also depend on ur heater - i cant remember what you've got.. but on my ram-flo one the tube for the screen passes between firewall and that card.. so its sorta.. moulded?! kinda!!
The best idea is not to use the same bases, because whatever the stuff is (papier mache??!!) it aint like normal cardboard and as you've probably found in getting them out they bend very easily. I would carefully strip the vinyl off and use the card for a template out of something more sturdy yet still flexible - what I dont know - but thats your job
Then just recover the vinyl - note that on my car the vinyl on the cards actually continues past the card and actually sticks on the a pillar, and then is covered by the trim strip that covers the door seam and door seal... ill post a pic sometime if i can be bothered
