I have created a spreadsheet that will create the market demand modifiers according to the environmental modifiers table as well as letting you have two adjacent markets (trade routes) alter each others demand modifiers.
In the other sheet I have made a spreadsheet that will take the hassle out of your PCs mercantile ventures. The only thing that I cannot do is create the roll tables for the likelihood of an available merchant to trade with you. This is the only thing left for you to do.
Please reply with any comments or questions.
EDIT: I have updated the spreadsheet, I didn’t realize that I forgot that the trade route tied markets did not have an option for equal market class. I have added this, not easy to miss.