Hi. Welcome to the TC forum. We have many honorary posters here. Please feel welcome. You are correct about the other forums in how and what they use their RVs for. This group is more; "How can I do this? Fix this?" Where many of the other forums are more inclined to; "Where can I take this to get XCVZ done?"
What you are doing will involve many things beyond the original design capabilities in your current van. Please remember this and work within the design standards. There is often a reason for many to choose to keep their Adventure vehicles, stock. Remember, when you are beefing everything up, you will need to increase the abilities to cool things (trans, diff and larger radiator/push pull fans). One thing so many fail to mention and do, brakes. You will need to stop at some time during the use of your vehicle. By checking what you have and the weight parameters will help you. There are many types of brake upgrade, whether bolt ons, swaps or as simple as changing the type of brake pads. Some just put bigger tires on and bolt on larger rotors.
You didn't mention what type of cold weather use you were planning. There is a huge difference in using a RV for going to a weekend ski resort or snowmobiling, camping weekend in the snow in Yosemite, living in it for extended times or fulltiming. When you are able to provide more background, I will be happy to help you with this portion. You are correct about condensation, mold, spores while wintering in an RV.
Removing voids, and outside surfaces is really important, for cold weather use. That is why dual pane windows is a must. Many Van Conversion suppliers have windows to swap out to. Also, spray on insulation will be the best way to eliminate the voids where mold and condensation will gather. The farther away your inside surface to the outside surface, the better in minimizing condensation on your interior.
Good luck, it sounds like you have an excellent project ahead. Just remember, it always takes many more days/months to put a project together, than you might have planned or imagined.
b