For us, it really depends on the destination, and your situation. Some trips we only eat at the camper, others we may eat out half the time or more.
If you are retired, and stay in the camper for long trips, you probably treat it more like at home and eat out sparingly.
We are both working, and have kids, so out trips are a week at a time vacation, and weekends. When we go to the beach we think about all the money we save staying at a campground versus $2-3000 for a condo for the week, we look at that as savings to do other things, eating out, go-karts, charter fishing etc. If we had to pay for a condo, we'd be eating baloney sandwiches :)