Really happy to see all the radio knowledge here, back in 02 I was on the NYT Circuits magazine discussing the WiFi boom. I had made an RF antenna out of an aluminum dog feeder dish of about 1.5 ft radius and a slight curvature which created a focus. In addition, I had created a reflector horn out of a soup can and made a dipole with some coax. I put it all together using a math formula having to do with the 2GHz wavelength and it worked nicely. I used a fiberglass pole to pick it up off the ground and insured that an open path down the driveway was available. just some thoughts, the open path is the best (as many have noted), if you have water for the groundwave propagation that is also very nice esp sea/ salt water. A nearby chain link fence will take out the ground wave even if it is not in your line of site (LOS). Just a thought added that every halfing of height is about a 3dB drop in reception. All things being equal, Getting as high off the groundplane is the best thing to do. Be sure that the base is sturdy as if you have a directional antenna wind will flex and move your antenna out of its max sensitivity and the link may break. The higher the gain of your antenna, the narrower your beam width (main beam 3dB gain point). Another alternative is to place the RV at right angles to the base antenna thereby letting the RV act as a reflector. The more metal in the structure the better, you can try aluminum foil or roll-able metal window screen mosquito netting. If you have a signal strength meter software on your PC/ MAC etc you can experiment with the placement, rotation by trial and error.
On 911 calls, this may help anyone with cellular phone as well. 911 will get through when voice calls won't because the cell phone companies will not allow you on if there is voice call insufficent quality. That does not hold true for 911/ the parameters for strength and quality are dropped as it is considered an emergency call. Put the phone out at fingers and away from your head, make call on hands free device or loud speaker. This may increase signal out to 8dB due to head losses from RF signal. If you know where your cell tower is located you may be able to put yourself out doors and on the side of the RV / reflector which has best coverage. You can likely hot spot your mobile as well if you can't get WI FI with a better signal if the mobile is being reflected into.
If you have any questions please feel free to ask I am an RF Engineer who works on cellphone systems e.g., NEXTEL-Sprint-TMO, Verizon, AT&T and also the equipment providers Ericsson, ALU-NOKIA etc.