Hugh,
Let me say that at one point I was the sole North American distributor for the German Wiesel 1 AWC. I never sold any, so that and a ten spot will buy me a cup of coffee at Starbucks. However, it did afford me an education in lots of bits and bobs.
First, figure out what your engine is rated to haul. Then halve that number to be able to haul it around under harsh conditions. Lots of early armored cars and tanks suffered from a fine automobile engine being stuffed into a vehicle at the upper edge of what the engine could carry. There were lots of overheated vehicles, and in some 1930’s reports you could follow an armored column doing peacetime maneuvers by following the broken down tanks and armored cars.
Second, look at layers of armor vs. a single monolithic block. To give an example, the side armor on a WW II M5 was on average 1 to 1 1/8 inch thick or 40 to 45 pounds per square foot. This was considered sufficient armor to stop all light arms and artillery splinters. This is using RHA or rolled homogeneous armor, which is still the standard that everything else is tested against. The current generation of armor, such as is used on the LAV-25, can provide the same protection using 1/4 inch of armor at just over 10 pounds per square foot. It does this by alternating layers of ceramic armor, modern alloyed metals, and spall liners. Considering that each side of a bus is roughly 40 feet by 10 feet or 400 square feet this is the difference between 18,000 pounds per side and 4,000 pounds. For the whole bus, this is the difference between 81,000 pounds for RHA and 18,000 pounds, and that is just the armor. It’s 9 tons vs. just over 40 tons.
If I were to be working on hillbilly armor I would use AR500 plate steel, design it so that it is sloped radically, only protect part of the vehicle, and then spray it down with Rhinocoat hard coat. Rhinocoat prevents spalling …
A 1/4 inch AR500 plate with Rhinocoat hard coat weighs roughly 9 pounds per square foot and will stop non-AP .30 caliber rounds. You are still going to end up with adding close to nine tons of weight to the bus if you armor it all over.
Your average-sized 55 passenger bus is designed to hold roughly 7 tons of people and gear. So empty of people, you are two tons over its weight capacity already. Reduce the armor on the top and the bottom of the bus, and only armor the driver’s area and maybe the first 1/4 of the bus. This should be enough room for 12 people or so. – H.D.