CB ground plane in Class C-revisited

I installed a CB a 8-10 years back and ended up mounting the Firestick 2 foot antenna to the top of the ladder at he rear of my Class C. It was a problem trying to get a ground plane. The ladder is aluminum and a poor conductor plus it isn't attached to the frame for a ground. I ended up running a wire from the antenna bracket to each side of the side rain gutters. That seemed to give me a good match of less that 2:1 on all channels. I removed the radio 18 months ago and put in a Ham radio. I haven't had much success with it in the MH. It is good for scanning.
I swapped out the Ham radio for the CB. I still have all the coax and power under the passenger seat for the CB. I tried to get the match down below 3-3.5 with no luck. I checked all the connections and cleaned the ground wire atop the ladder going to the rain gutters. That improved it a little, but it's still around 3:1. There is a sheet of metal on the floor bottom running along the length of the MH to the engine compartment. Do you think running 8 or 10 wire from the antenna/coax connector to the frame or the metal floor protector would help?
We are going on a trip and I will need the CB more than the Ham Radio. Yes, I tried a No ground plane antenna with no luck. For some reason which I can't recall I switched it out to the Firestick.