You could probably use the MegaSquirt MS2 or MS3. Inexpensive, just don't need the fuel control. In addition, you could use the spare I/O's to run an electric cooling fan or something else cool.
I am very hesitant to use an aftermarket setup that cant be easily bypassed or switched back to stock when I might find myself stranded in the middle of no where 1000 miles from home in my RV.
How reliable is the megasquirt stuff? Is it difficult for a complete novice tuning the set up?