I've used boards for the last 30+ years and they have worked fine for me. I have 4 2X6 planks with tapered ends and 2 of them are a little shorter than the other 2 so I can stack them if I need to. Very seldom, and only if that was the only way possible to get level, I have lowered the corner camper jacks and lifted enough with them to level the camper but only if that was possible without lifting the camper off the truck bed.
The hazard in using the camper jacks, or any other jacking system, is that driving away with them down is a possibility. For me it would be more like a probability.:-)) If I did something like you are suggesting, I would also include a warning of some kind in the truck to alert me when the jacks were still down.
It will be interesting to find out what others have done, and what you decide to do.
Thanks for starting this thread.