What size vac pump are you using?
Hello David. For building my F-85SR I am using 2 pumps, both 3/4 hp. Theoreticaly they can handle 226 Liters/minute each. The exra pump helps if you have a small leak, so you still can have a reasonable pressure. One of the pumps runs via a pressure switch. It switches off when a pressure of around 0.7 bar / 21"HG is reached. My pumps are of chinese manufacture and use quite a bit of oil, to the point that I have made exhaust tubing to lead the oil outside. But it works well.
Phill is a great source of information. I can't match his building pace but it is nice to exchange information and profit from his extensive building experience and knowledge.
As to building costs: Some builders have gone to cheaper foams to keep the cost down. My advise is to not go this route, but use the best there is: Corecell M ( IMHO ...
) I spoke to several F-82 builders here in the netherlands who went this route, but in hindsight they now say they would have done otherwise.