lol.....just to confirm...it IS oil....and it may effect your paintjob......and if you are coating it with resin, the resin might not be able to penetrate the cardboard and may result in a weak spot that will crack easily.
Another thing to be carefull of is using fire retardent upholstery foam next to your skin as the fire retardent stuff tends to be cyanide based and your skin might absorb it........so best to try and cover it with something......or make sure you use the non fire retardent stuff.
Good luck with your project.