When the epoxy isn't 100 percent cured, you can get a better result with a scraper than with sandpaper.
I have seen a gadget which used a vacuum diaphragm thing, working against a spring, to switch the vacuum pump on and off. I think the diaphragm thing may have come form a carburetor housing or whatever we used to call them, and would take warm air from a shroud around the exhaust manifold when the engine was running slowly and it was cold. It pulled a threaded rod against a spring. On the threaded rod were a couple of tabs held by nuts which poked at a small switch. That way, even if there was a leak, the pump wouldn't run all the time. Here is a similar switch:
https://www.glide.net.au/flyingwing/vacbag/index.html
Best with a vacuum reservoir. I'm guessing an old, small propane tank would probably be good for a vacuum reservoir. (Kind of funny to call it a reservoir, since there's nothing in it.) I've seen a 55 gallon drum used that way, but it turned out not to be strong enough. I understand it was pretty loud when it collapsed.
BTW, if the vacuum pump sound is annoying, run the exhaust through a line into a sealed jar or other fairly rigid container, with another tube coming out of the lid. Acts like a muffler, and, if your pump is the kind that spits oil, will presumably trap oil.
BTW, what's cheap and available that makes decent vacuum oil? I have an ancient vacuum pump in my garage, and I want to make a big bell jar so I can dry wet boots or potassium nitrate, degas RNX, and stuff like that. At least after I dig down deep enough to find it again.
