Well, cant help ya on the buggy, but why not score a used kids backyard slide for a chute? Seems about perfect to me. Set the thing up right below that window, open window, slide the BTUs down.
or maybe an old water heater...torch the ends off.
@ the OP...whatever you decide, make it something you can use for other tasks...if it's a one act wonder, it better be pretty darn wonderful. (like, save you 6 days of back breaking work wonderful...or have a cup holder:msp_tongue