Have expel on the Z for 8 years, on the M235 for two and now the M2. Love this material. Now others may differ but here is how we do it:
1. Wash carefully with a good non detergent car wash...two buckets is always best. Always use a clean microfiber mitt. Just don't use dirty or rough sponges. Care taken on the edges of course.
2. Good rinsing process.
3. We wax with a good poly wax...several on market. I happen to like the Griots, but each to his own on this. And I use an orbital for 2-3 layers of wax. Removal and hand buffing.
4. Then top it with some regular sacrifice barriers of spray on wax each time its wet or washed. These extra barriers protect the base wax layers.
5. Treat it with some care, and it lasts just fine.
Hope this helps some...others may differ but no one will disagree with some common sense care on the surface and at edges.
I noted on the M235 on rocker panel, a very fine line of dirt about 2 inches long had developed. Very thin and not deep into the film. My dealer who is meticulous, took a very fine razor and trimmed the film back a bit, thus removing the dirt line that had developed -- and could be seen on a AW car--and took the film back to its proper adhesion level there. Looks and is fine and tight now.