I'm quite familiar with the condition. My collie has seizures and is on a couple meds (phenobarbitol, KBr). We've tried Keppra and Zonisimide with no effect. Fortunately he usually only has focal/partial seizures most of the time, but will have the GM type 2 or 3 times a year (had one yesterday, in fact).
One thing to consider is adding MCT (Medium Chain Tryiglyceride) oil to his diet. A veterinary neurological study showed improvement (not elimination) of seizure activity with a ketogenic diet and a diet high in MCT's. Purina prescription now has "neuro-care" available through vets - it's basic low quality purina food with MCT added. I started using MCT oil (derived from coconuts) since April and the seizure frequency has basically been cut in half. The oil is inexpensive and available on Amazon (I add about 2 teaspoons to his evening meal).
Some have used CBD oil (cannibus oil) with mixed results. Also, one medication we haven't tried yet is gabapentin which appears to be effective in some dogs.
It's bad condition to have to deal with. Obviously for the pet (cats can have it too) but for the owners. It can be stressful watching/waiting for the next one to occur. My biggest concern is being away when a GM occurs. My dog becomes very disoriented and uncoordinated for a while after the convulsions and I fear he'll injure himself falling down or bumping into things.