When confronted with this situation, we routinely put our portable GPSMap 76 in the Oven of our stove in hopes that it will survive any EMP effects.
Same here. The oven becomes a makeshift Faraday cage for not only a handheld GPS, but also the handheld VHF, cellphones, laptop, etc. It gets a little cramped in there, but we make everything fit. So far we've never had lightning stikes close enough to prove the efficacy of the oven as a Faraday cage, but it can't hurt and may make a life saving difference.