Black Rock City back-pack
Your major problems besides COST are:
1 Fuel type: what do you want it to do vs. want it NOT TO DO.
Pressurized gas/vapor vs flammable liquid.
2 Storage/reservoir/re-fill: how do you get it into position.
3 "Throw" it: pump, pressurized tanks, catapult?
4 On-Off without "spray" (self immolation) or too much dripping,
or a place for burning drips to NOT be a problem.
5 A way to keep it lit. A BiC lighter will NOT work.
A small propane jet under the nozzle?
6 What-to-do if/WHEN you spray (your Skoolie roof) an area with
highly flammable liquid just waiting for a spark.
7 FIRE SUPRESSION !!! 4 guys with extinguishers are priceless.
Who are you going to share the flames with other than buddies?
One problem with propane is pressure. Another is VOLUME.
Otherwise your efforts may end up demonstrating a large BiC lighter...
Also, you can't just re-load propane just anywhere.
The picture of the 'British kid' shows LIQUID burning, not gas/vapor.
That is more of a flame-THROWER vs. a big lighter.
I saw a Back-pack on the Playa using cornelius kegs (soda kegs) commonly used in HomeBrewing applications (I have some myself).
They are "inexpensive", can take high pressure, and are easy to fill.
Check your o-rings in case your fuel eats them. I have never tried
the flame-thrower thing, but have thought about it, as you can see.
Those guys used Kerosene for its less explosion-prone properties.
They powered/pushed/PRESSURIZED using Nitrogen as it is relatively
inert, inexpensive, and resists going into solution. Using CO-2 yields
carbonated flame-thrower fuel, bubbles, and Co-2 bubbles at the
flame site decreases Oxygen needed for combustion.
I did see the "Moby Dick" with a water cannon (?) mounted on its roof.
During the day they could pump water so it could cool BRC residents.
At night they sprayed fire upwards about 10-20 feet, nothing ever
touched the ground, or roasted other 'burners'.
I guess that this would involve a pump, reservior, starter flame,
and a considerable inve$tment over the Corny Keg personal unit.
Have you considered military surplus, E-bay?