I don't have a dual band radio in my RV, just in the truck so I use a regular 5/8 wave mobile VHF antenna and a Hamstick for HF.
I could use a UHF/VHF dual band antenna on the mount but don't need it. The following picture shows how it is mounted. Oh by the way the VHF works fine, the HF could stand a better antenna but who can afford one of those fancy ones.
VE7HD - VE7VCR (repeater and IRLP Node #1503