I've not installed one in an RV, but have in our home. As you could imagine, a lot of heat builds up over the unit from the convection. If it says 4 inches, it's every bit of 4 inches. My only suggestion is contact the manufacturer or the dealer to see if there is alternative venting you can install.
Bottom line, these units get hot, even on a 110v line.
2017 Ford F350 Super Duty 6.7 King Ranch Crew
2016 Crossroads Sunset Trail Grand Reserve 32BH