It is unlikely that if your camper cooler is left open, there will be enough humidity for the magic to happen. For pinning and fruiting you will need 85% humidity or greater, I often use ultrasonic humidifiers to push into the 90-95% range. If you are looking for stealth, do a monotub style grow except use an opaque tub, then keep the lid on tight and attatch a florescent light to the inside of the lid. Route the electric cable toward the back so it is out of sight, and voila! Full scale mono tub with no light or noise.
Also, pf cakes are for kiddies, purposefully designed by commercial growers to keep people like us from really getting decent harvests. Don't follow in the foot steps of 14 year old kids, use grains, WBS is cheap and easy, cracked corn can be used in half pint jars for super fast colonization from spore, then transfered to WBS for potency. Bottomline, do not expect anything that coule be labeled "bulk" when using pf cakes.
Good luck, I hope everything works for you, by the way, even a very small harvest of Penis Envy is worth while, so if you insist on growing cakes, use penis envy so your tiny harvests will atleast get you high!
b*real