Just chiming in with my 2 cents as well. I always try not to be too hard on sales people as they couldn't be expected to have much expertise with all of the tools and technology available. I think most are genuinely doing their best to help customers solve problems and are really not in it to just make the sale.
There is some really good information in the prior posts about heat and pressure. I can only comment based on my personal, and somewhat limited, experience with casting. First of all, for blank casting I have only used Alumilite Clear Slow which I think may help with reducing bubbles as it is in the liquid state longer so there is more time for bubbles to float to the surface and more time for the pressure from the pressure pot to do the magic it does on them. As for epoxies and other kinds of resins, I simply don't know.
I have been successful without heating my molds. I use homemade molds made of Schedule 80 PVC pipe and I just haven't found a simple enough way to heat them up before use. Maybe I'm missing out on something and will figure something out some day, but so far - so good.
I use a 2-1/2 gallon California Air Tools pressure pot. I never had a Harbor Freight pressure pot, but I know it is designed for use as a paint pot and not as a pot specifically for casting like the California Air Tools pot is. I know it was about double the cost but from my experience, it was nice not having to fiddle around with the plumbing or anything else. I have also heard that some folks struggle with getting the Harbor Freight pots to seal well, but that's just hearsay. My California Air Tools pot has worked just great - right out of the box.
And, finally, casting my own blanks has been a thrill. I'm so glad I decided to jump in and only wish I had done it sooner. It's been great fun with more to come.
Regards,
Dave