I had that happen before,I pulled the carpet and it was like Joes apartment in that bitch,and it was'nt the big one it was little Nazi SS German ones.What I did just because the car was completely gutted and since I had to clean the interior out from where the carpet was wet it left nasty brown sticky crap,I got myself about 10 cans of brake parts cleaner,gloves,goggle,and a mask and went to down on those little bastards.In your case id get a bunch of roach bait and spread it around the car,cleanup might be messy but they wont be crawling on you.