If your roof I what is commonly referred to as a "rubber" roof you will not find the product in Mexico. However if the material is more or less intact an has gotten thin you can find all kinds of "impermiabilizante". These are Elastomeric coatings. Comes in 5 gallon buckets. There are various qualities and they are rated by "years". You can also get a fabric that you lay down on top of a wet bed of the product for reinforcing. Can be applied with a roller or brush. If there are any tears in the roof I would use the sealant as a glue for the tears and make sure you cover that tear with the fabric. Easy and quick to apply. The roof should be clean. Make sure that the wood under your roof is not soft or sagging. Also do not apply the sealant too thick. It is heavy! Any paint or hardware store carries the sealant. Home Depot as well. There are all kinds of entrepreneurs that will do the work. Make sure they do NOT thin out the material with water. Famous Mexican trick! I hope you do not plan on towing this unit back to the USA.
Moisheh