I have been doing chassis edges for years. I have done many pro drivers chassis.
The drip method is the best.
I don't sand the edges. I use a sharp diamond file to lightly bevel the edge.
Then clean all the edges with denatured alcohol.
I then take a permanent magic marker and black out all the edges.
Wait one hour. Then use the drip method and hang the parts over night.
Do not over do the glue or you will end up with white discoloration on the chassis.
Hara had posted this method a while back and it works quite well.
It just takes practice to get it looking perfectly smooth.
***Team driver for Team Associated, Reedy, A-Main Hobbies, Lutz RC, Alpha Engines and Integy***