What should I do?

Working on a project in cold climate need to insulate under the building. The building used to be a s summer house, so it has no insulation under the building, there is no basement and almost no crawl space. It starts with 2ft of space and then gets smaller and smaller to the point where there are only 10 inches of space left. How do I go about finishing this job? Is it possible to use spray insulation there? There is also no vapor barrier so moisture penetrates trough the floor and is slowly destroying the wood under the building. What should I do? Try to spray insulation and do the best I can or invest some money and time into digging out dirt for a bigger better crawl space? If anyone has some experience or advice please share