I have tried this same code on Rhosimulator and MC75 WM device and i am not able to recreate the issue,
I have created new Rhoelements project on RMS4.0 and have given the reference link to your index.html in index.erb. On clicking the link it loads the index.html correctly . I have not observed the blank page issue. Let me know if any other step i need to follow.
In your code i have seen<body> tag written twice.
I was getting the same issue running in RhoSimulator ( via rake run:wm:rhosimulator) but your observation concerning the two body tags was correct i.e. I removed one of them and it now works as expected. Thanks for your help with this!