Regarding squats, I've read a few posts in the forum that mentioned back fatigue when discussion was at a higher rep range. I believe the big quad guys advocate higher weight and lower rep citing back fatigue as a possible issue. I too have a severe back injury and get lower back muscle fatigue. What I believe has helped is using 1 or 2 front end sets between 30-50 reps with 135 then going in to my heavy pyramid of 5 or less reps. I usually finish with a drop set starting heavy. Yes this fatigues the hell out of you, but I believe this helped me increase stamina in my lower back. My goal for this was to make my back adapt knowing the fatigue was a weak point. I also do not wear a belt.
I've never done Romanian dead-lifts though...I started doing traditional dead-lifts and rack pulls several months ago under a fear of what might happen with my back. I actually detailed it in an older thread. With the exception of the front end sets, I've been following a similar heavy pyramid routine for both and it has greatly strengthened my lower back. I'll give rdls a try soon and see what happens.