Most convection ovens do not have to be vented to the outside in an RV, but they do require some air space. BTW - my cooktop/ oven in in a slide - and it doesn't vent to the outside either.
Your regular over in likely 21 1/2 inches wide. The Dometic 1100W Convection Microwave we added to our TT is 22 1/2 inches wide. We had to alter the trim (cut it away) to have room for the Convection/Microwave.
One thing to consider - without an outside vent - the convection oven will add quite a bit of heat to the inside of the trailer. We've baked whole chickens, steaks, cookies, biscuits, etc in ours - but mainly in the winter.
While the convection adds quite a bit of heat in the summer - it will cook almost anything an oven will - and a lot faster than the over - especially if you use a combination of microwave and convection. So the net heat increase is smaller in my experience with a convection than a propane oven.