Nuclear initiated EMP events are by nature, low in frequency (below 100 MHz). The estimated energy of such an EMP event is less than 1 J/m2 at the ground level. Antennas and power lines are the major collectors of this energy. Due to the low frequency nature of the EMP spectrum, an 80 meter dipole could deliver a 1 MV pulse to the feedline. The best protection for your VHF radios is to simply remove the antenna and any other cables since these act as collectors of EMP energy.
The aluminum foil may actually increase the susceptibility of the radio to EMP damage if not made and maintained correctly. Here are a few of the basics: The skin depth in aluminum at 1 MHz is 82 um. It is considered best practice to use a material with at least five times this penetration depth or 410 um. Common household aluminum foil is 16 um thick and heavy duty household foil is 24 um thick. As a result, a generous portion of the 1 MHz energy will pass through the foil. This effect is multiplied by the fact that larger surface area of the foil allows it to more effectively couple to the 1 MHz energy. The net result is that more 1 MHz energy could be coupled to the radio with this faux Faraday cage than with simply leaving the antenna jack open circuited.
Regarding antennas and range, keep in mind that on VHF, most of the communications takes place on a line of site basis. You may get "lucky" and get just the right reflection or scattering from the geography or man made objects but this should not generally be relied upon.
A few watts EIRP will allow point to point communications on VHF with line of site conditions. You should first focus on height of the antennas and then secondarily on gain. The gain of the antenna may help you overcome minor fringing, foliage attenuation, and interfering signals or noise sources but it cannot typically and reliably make up for a blocked line of site. Put another way, you could invest in expensive, high gain antennas and still not be able to reliably communicate without line of site conditions.
There are two approaches you can take. You can do empirical work by experimenting with various antennas and antenna heights. This could be done with some simple home built 1/4 wave ground plane antennas placed on extendable painters poles held up by hand. Once you have communications, experiment with the power level and height required to maintain the link. Keep a log book of the results of your experiment so you can translate this into the final solution.
The alternative approach is to study the topology between the two locations in order to reach some general conclusions. An on-line topographical map and a drive through the area can be quite instructive. Once you have a sense of what should be possible, you can then proceed to experimentation to verify your findings.
