Since you already have DirecTV service and receivers you just need to bring a box into your RV, attach an appropriate antenna and sit back and enjoy.
Can you tell us what model number DTV receivers you have at home? Be aware that there is NO dome style antenna that will allow the reception of the DirecTV HDTV programming but ALL of the SDTV programming comes from just 1 satellite making that reception very easy. The reception of your Network TV programming can also be an issue depending upon the antenna you use and how far you plan to travel from home so any additional details about your plans would be helpful.