I've been putting together a spreadsheet for design of some fairly simple vessels. But even that design very quickly gets very complicated before it is done.
I've really not seen a good solution. Plugging numbers into a program and saying "I guess it's right, or they wouldn't have sold it to me" doesn't seem to be the ideal solution. Checking something like that gets very involved, and is actually more involved when you're checking someone else's work than on your own.
Note that in addition to the code calcs, you have wind, seismic, saddle design, local nozzle loads, etc., and those items are not codified to the extent you might expect, and allow for a lot of variation in the design.
There are similar issues with tank design software, and from past experience, I have found that it can be out-of-date, wrong, limited in unforeseen ways, etc. Maybe the PV field is better in that respect.