You will not need a new antenna; just the converter box.
Always use the amp when using the roof antenna.
Turning it off disconnects your roof antenna.
Nearly all new digital channels are on the UHF band. The antenna head on your camper has "wings" to receive VHF (making VHF reception directional) and an OMNI UHF (equal - but poor - signal all around for UHF).
Winegard - HDTV/DTV Reception Basics
Adding a winegard "Wingman" can help you by boosting the UHF signal with vanes that "warp" the incoming UHF digital signals onto the existing UHF antenna head. This will make the UHF antenna ALSO directional. You must then point the antenna head AT the transmitter of the station you want to watch.
Winegard Knowledge Base
You can get the compass heading to the stations in your camping area using this web site IN THE US. I don't know if there is a similar one in Canada. www.antennaweb.org
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW