I did some checking on this ant problem. I am told there are 3 things to use,
1. Ortho Home Defense....This is suppose to be the best thing to use
2. Terro Ant Killer
3. Food Grade Deatomaceous Earth....I don't know what this is, but I use Deatomaceous Earth or it is also called D.E powder for my pool filter, I don't think it is the same. So far I have not had any problems with ants, but what I did was put ant traps under all of my cabinets and even in the storage areas. A good place to protect is where the city water connects to your camper, If the hose is on the ground with one end connected to the water supply and the other end is connected to the camper the ants will use this as a bridge to get in around the connection. If you can access the back side of the city connection then you may want to inspect this area from the in side to see if you can see any light from the inside if so then you may have to re caulk the area. The other thing that can be done as well is to treat the ground where hoses and power cords are laying that's connected to the camper.