I am getting ready to start putting the car together. Do you think it would be easier to install the hatch glass with the hatch on the car or on a table? I am thinking it would be easier with the hatch mounted on the car. 

Much easier on a table.... unless you are a contortionist 😉

Also, having the hatch on a flat surface with make installing the stainless trim much easier as well.

Definitely a table, make sure you also install the SS trim as well before installing in the hatch.

I have done the hatch seal twice while on the car. Wasn't too bad but had someone on the outside pushing down on the glass slightly when needed. I did one hatch seal on those X shaped saw horses while pulling the string down towards the floor which wasn't too bad either.