Skier Need Help Choosing Home on Wheels

Hi there! I am a competitive skier from Washington looking to live out of a vehicle full time, but have had a lot of trouble over the past year trying to decide what vehicle would work best for me. My main priorities are that the vehicle is 4wd, has standing room, and can be well insulated and heated for living out of ski area parking lots. It would be nice to have a shower, toilet and decent gas mileage. Stealth could be nice as I may be in and out of Seattle for my engineering job, but I’m not sure it is a priority as I have friend’s houses I can park at. I am a mechanical engineer, so I am open to building a living space on my own, but am also hoping to have starting costs of no more than $20,000. The vehicle will mainly be used to live at various ski areas I am competing at, but will also be used in the summer for climbing, biking and mountaineering adventures. I am considering the following options: Truck w/ flatbed or slide in camper (open to custom build option), truck w/ trailer, euro style van (ram promaster or ford transit, ford econoline, or an ambulance. Any and all help deciding is greatly appreciated!