I assume you have checked that the booster is on in both units. Are they the same antenna make and model? Wiring in good shape? If so, it could be the TV in the Winnie. I have two HDTV's that are used in my MH. Two different brands (both low end). One is permanently mounted to the dash the other I use outside from time to time. The one outside acquires fewer stations than the inside TV. I have tried hooking them both to the same antenna feed with the same results. They may have different spec's in regards to what signal strength is acceptable in order to be acquired during the channel search.
As a second input, I swapped out the original Winegard Batwing (12 yrs old at the time) for a Jack. Big improvement. Did not alter the fact that one TV picked up more.