Your best option using an external antenna would be to also use an external amplifier if one is needed. Assuming you have one of the common Winegard OTA RV antennas, the amplifier is actually located in the antenna "head" on the roof, not at the switch plate that turns it on and off. With a residential style multi-element antenna mounted as high as practical and correctly aimed, you may not need any amplification at all with the signal connected to you RV at the "cable" input connection and the inside antenna switch turned off.
Dutch
2001 GBM Landau 34' Class A
F53 chassis, Triton V10, TST TPMS
Bigfoot Automatic Leveling System
2011 Toyota RAV4 4WD/Remco pump
ReadyBrute Elite tow bar/Blue Ox baseplate