Wow! I did not realize there were so many options available out there. I built my setup without getting advice or opinions from a Forum. Maybe I should have done more research.....but, my system has never failed me. I built a setup for wifi and cell service and I have been using it for about three years now.
On the exterior, I use a Tripod that I can bungee cord to the ground. (It stores away easily and is out of sight.) On top of the Tripod I mounted a Omni Directional Cell Antennae from http://wilsonelectronics.com part#301133. The antennae cable is small and runs to a Wilson Dual Band Amplifier (SOHO) Part# 801245. Then, a cable runs to a permanently installed directional INSIDE antennae that distributes the cell signal throughout the full 40' length of my RV. The dual band allows for Janet to chat on her cell phone while I use my AT&T card in a Linksys Access point (model#WRT54G3G-AT). There is one point you should know. The Wilson setup uses a external antennae and a inside antennae. Normally, the two have to have at least 25' separation or oscillation occurs. But with the inside antennae being directional, that distance drops to 10' as long as the inside antennae has it's back to the outside antennae.
Now, back out to the Tripod. Under the Wilson antennae, I mounted a Hawking Technology http://hawkingtech.com 14db gain Outdoor Direction Antennae (Model# HAO14SDP). The cable runs directly to my network card in the computer. (No amplifiers or power required.) I looked at amplifiers and found that they only amplify what the antennae is able to receive or transmit. I suggest a directional antennae MIGHT be just as good as a amplified omni-directional with less expense and no power requirement.
The only hassle is pointing the antennae around until you get a signal. Janet usually sits on the computer looking at the signal strength while I rotate the antennae. It almost always get a full meter from somewhere. There are USB net cards that allow for a external antennae hookup and Hawking sells everything you need.
Another thing is that I run the two small cables in a window. I have been meaning to permanently wire the interior and install two male connectors to the exterior wall of the coach. This way, I could setup the Tripod and simply screw the antennae cables to the connectors when I want to use the antennas. A rubber boot could be slipped on the connectors when they are not in use.
Cost for all of this was about $750 but I notice prices have dropped since I bought everything.