To convert a bus into a motorhome, list the items you need in your space and sketch a plan to find out how to fit everything in. Remove the interior seating to create an open space to work with.
Before adding items to the bus, consider your insulation options. If you plan to use your bus only part-time and in temperate areas, you might want to pass on insulation, but it's essential for full-time living in most regions. Foam insulation is a good choice, but also consider thinner insulation panels that take up less space. Strong glues work well to secure panels to the walls.
Determine which heating or cooling solutions you want. Most fuel-based heating options require ventilation, and air conditioners generally need to sit partially outside, so determine where to cut out part of the bus. You also need to determine how to generate electricity; solar panels are a viable option, and extra batteries are great for infrequent use. Install any water tanks you need, and make sure you can dump your gray water and black water tanks.
Small appliances work well in buses, so consider using small ovens, sinks and other kitchen items. Decide how much space you want to dedicate to sleeping and how much you want to dedicate to space for working and relaxing. Convertible furniture is a great way to reuse your limited space.