I want to get about 45 min of working time but the best I've been able to get is about 20 min. Any tricks to slow down the set time??

Twenty minutes is pretty good - you may try less hardener in the resin, but I dunno about stretching it 45 minutes...

What are you trying to do?

S.

You might be able to get a slower curing resin through someone like Aircraft Spruce & Specialty...they offer free catalogs (HUGE...they even have a race catalog now too!)
http://www.aircraftspruce.com

You could use a little less hardener/activator, but that can only buy you a little time...too little hardener and you weaken the part. I have never timed how long mine lasts, but I doubt its even twenty minutes.