Let me preface this by saying I'm a believer in seat belts- they saved my life once.
I also believe in assessing things like risk and reward rationally. Case in point people have fear of flying, but rationally it is safer than driving.
To the point, what is the risk per mile travelled in a MH compared with other activities, specifically car travel?
This guy did some nice work which seems sound. You can Google up all the numbers for yourself if you're so inclined (I did). His conclusion is that motorhomes have on average one third as many fatal accidents per mile compared to the overall vehicle population.
From that, I can draw the conclusion that I'm safer in the MH than the toad, so belted in the MH is the best choice. Less clear- is driving the toad (belted) safer per mile of travel than being on the bed or the dinette in the MH?
According to NHTSA the fatality rate for school busses is only 0.2 per million miles. A great number, not because of belts, but because they are big and yellow.
Maybe Hi-vis yellow MH will be the next big thing. :)