If it's a bad Idea to keep my 2 raspberry Pi's inside the enclosure.  I ask since I am told that at least with PETG it off gasses pretty nasty stuff and Im worried that it will gunk up my pi's and kill them.  Also with the heat that this will create would that be a issue for the passively cooled boards?

ABS is the one that off gasses.

I'd be more worried about temperatures for the Pi, over the off gassing ABS.  With ABS, you generally want a warm enclosure, which might cause thermal issues with the Pi.  IIRC, above 60*C, the Pi starts thermal limiting.

Gasses aren't a concern.

You'll likely be fine if you aren't actively heating. Actively heating and I'd be relocating the pi outside the enclosure.

yep.. i keep a thermometer in both enclosures, and the 220x220 ender 5 pro gets up to about 90-100 F stable, the much larger footprint 5 plus (350x350) runs about 110f up to 115f depending on ambient.   That's passively cooled by the print bed, not counting any active heating i might apply also for PC for example.  

Separately i posted a thread a while back about raspi 4 temp graphs from my raspi microcomputer box project -  uncooled, active cooled, or passive heat sink and i'd say it would not be good to run a raspi 4 or above in the enclosure except with an ACTIVE cooling e.g. heat sink with fan.

Are you saying the RPi's will be in a printer enclosure?  Or they will be in printed cases?

I have 2 RPi 4s in PETG cases with POE hats, no issues.  Also have two RPi 5s in PLA cases with coolers with no issues.  None of the 4 are in the X1C enclosure.