You have some decisions to make.
You can take a receiver from your house to use in your RV (fairly cheap, but if you camp outside the "footprint" of your local channels, you don't have ABC CBS NBC FOX). Or you can establish an RV account for your trailer, and get the national versions of ABC CBS NBC FOX nationally anywhere.
Do you want to buy an automatic dish (expensive) or a simple dish and tripod (fairly cheap) that you setup yourself. My understanding (tentative) is that there is not an automatic dish at this time that will get DTv HD signals (only SD signals). If you go the cheap route, you will probably have to get a fairly expensive meter (~$240 and up) so you can get good signals on the HD satellites. A fairly cheap meter, or maybe none, is needed to get SD signals only. Some can get HD signals without a meter, but not me.
On the outside of your trailer is (probably) a TV cable inlet. It connects to your amplifier and through that to your RV TV antenna. Your satellite setup will not work like that. There is probably a short jumper on the inside of your trailer that connects that inlet wire to the amplifier. To use the inlet for satellite reception, you disconnect the jumper wire and connect your receiver to the inlet coming from the outside. If your trailer does not have such a jumper wire, you can install one yourself if you want to.
In my opinion, a very good source of DTv information is this site:http://www.dbstalk.com/forumdisplay.php?f=82
There are lots of people there who do exactly what you are wanting to do.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch