We just put one of these in my buddies RZR and it works great! Not sure how it would fit in the Honda.
Mojave Heater Part #640
The MOJAVE heater is designed to simplify the task of providing heat and comfort to your ride. It eliminates the need to locate hard-to-find parts, or go through expensive rebuilds to get old units in working order. Its design offers several mounting options, and the optional Plenum includes adjustable louvers and a flange for defroster ducting. The Mojave gets it heat from the hot water in your vehicle’s cooling system (just like an O.E. unit), but has the advantage of fitting into a wide variety of confined spaces. Its compact size, ease of installation and operation make it the ideal replacement unit.