Is your Direct tv satellite dish located on your RV or at some other stationary location? If it's at your house, etc. you need an internet connection and router at that location to send your tv signal from your satellite box to your Slingbox to your router, to your internet service provider, to SlingMedia. You will then use your laptop and wireless broadband card to log onto the internet to download and view your tv signal from the SlingMedia internet site.
If your Direct tv satellite dish is located on your RV, I believe you can simply plug your Slingbox into a router to broadcast the signal and use WIFI to connect your laptop to your router to view the signal.
I have a CradlePoint MBR1000 router that I like very much. You can actually plug your wireless internet card into the router and then connect your laptop to the router using WIFI to access the internet. Sometimes that works better than plugging a wireless internet card into your laptop.
Let's separate this into two issues. First is viewing your Direct TV and second is accessing the internet with your computer.
Obviously, you need to have your satellite dish properly aligned to receive and view a good signal whether watching on a television or using your Slingbox to view on a laptop computer. That's a given.
When you install your Slingbox, you will connect your Slingbox to your satellite box using component cables for video and R/L audio cables. Then, you will connect your Slingbox to your router using an ethernet cable. Now, you can connect your laptop computer to your router wirelessly using WIFI and watch tv on your laptop anywhere within 30 to 50 feet of your router. To do this, you are not using the internet and don't need an internet connection.
You will use your broadband card to connect your laptop to the internet. You will need a good 3G signal from your internet provider (AT&T or Verizon, etc.) to do this. You can insert your broadband internet card directly into your laptop or, if you prefer, you can insert the broadband internet card into your router. If you want to insert it into your router, you need a router that is designed to accept a broadband card, such as the CradlePoint MBR1000 I mentioned before. If you do it this way, you will be able to connect your laptop wirelessly to your router to receive the internet connection. You can connect multiple computers at the same time, instead of just one. I find that my 3G broadband internet connection (Verizon) seems to work better when using a router instead of just plugging the card into my laptop. One reason is I don't have to use the VZAccess software that is somewhat problematic in itself.