rox:
I have to agree with Egon that I think costs are going to balloon on making the modifications you want on the shipping container.
OTOH, if you are dead set on a container, here are some thoughts.
1. You can get containers with full-size doors on both ends. This eliminates the need for any roll-up doors. You may even be able to get one with full doors on the ends and a man door in the middle.
2. If you are only going to use it for a few weeks per year and only for 3 years, don't bother to insulate it. Sure, there will be heat losses, but most insulation has a payback time of several years. The cost of the insulation will be much more than the savings on heating costs for this kind of limited use. Just jet a salamander heater and use it as needed. This also saves on interior finish since the metal walls are probably OK as is.
3. Try to support the container high enough to run your pipes and drains on the surface under it--much easier to install. Give yourself about 18" of clearance so someone can crawl under to repair the plumbing under it as necessary. Insulate the pipes under the container and I doubt they will freeze. If necessary, block air flow under the container. See if the container is strong enough that you can use your tractor to build a dirt and gravel ramp into and out of the container at each end, both to support the container ends and to provide a path in and out. You may need a dirt mound crossways in the middle of the container.
4. The bowl-shapped floor is going to be a major issue. The least expensive thing I can think of is concrete with a steel-trowel finish. It is smooth and slick and they may let you get away with just that. Instead of a V-shapped floor with a central channel, think about dividing the floor into "cells" say four 10' long by 8' wide cells, each with a slight funnel shape and a drain in the center.