This is the type of Surge Guard we use - but even with the Voltage Regulator it tends to trip a lot in Mexico. These can be found at RV parts stores such as Camping World.
http://trci.net/products/surge-guard-rv
They also have Voltage Regulators but the ones they make only correct low voltage - whereas the ISB in Mexico corrects both low and high voltage.
The problem with a surge protector in Mexico is there is a built in delay in most of them to protect the AC unit - whether you have one or not - the delay can be up to 3 minutes. So what happens is you get a split second surge and then have to wait 3 minutes for the power to come back on.
What the voltage regulator does is give you a relatively clean and even 120 or so volts which makes equipment happy. Continual low or high voltage can cause equipment problems and eventually the equipment will fail. Nice even voltage can increase longevity of equipment.
There could be surge guards that do not have the delay but we do not have one as we do have AC units and want them protected. Ours is built in so it is there all the time no matter where we travel. We sometimes turn it off in Mexico. But we still use it for all other travels.