That's a really good idea... How big were the side vents? And of course, do you have a picture?
I had to move my shore power plug location while configuring my TD for real camping, I didn't know what to do with the 1.5" hole in the side of my TD, then I found a left over bath tub vent in my plumbing tools bag.
so now my permanent vents are a bathtub vent/drain cover (you know the one with the little handle sticking out of it to operate the drain on some tubs) they also sell them flush for those of us who prefer a manually operated drain plug (more sanitary to take a bath, have you ever seen the gunk inside the drain pipe, if you take a bath your'e stewing in that gunk)
I glued a piece of screen over the inside of the hole. I happened to have this vent left over from another project, I figure if it is made to withstand daily showers, it should be fine on the outside of the TD. One of these down low and one up high on the other side should keep me alive.