I'm in a very similar situation, and I'm using a Roth as a temporary location for some of my emergency fund. It's a good thing to do if you can't max out tax-advantaged accounts this year, but will be able to max out these accounts in the future. It's a temporary location for your emergency fund because in a future year, you will build up an emergency fund outside of the Roth after you have maxed out all of your tax-advantaged accounts. (And at that point, you can consider the original Roth funds an "investment" and part of your asset allocation, rather than as an emergency fund).
I'm not sure if I'm tracking the "selling at a loss" point. Presumably, inside your Roth IRA, you will invest in whatever vehicle you would have chosen if the funds were not in the Roth. So I guess the fear of selling at a loss might be a reason not to invest your emergency funds in certain vehicles rather than others. But I see this as an independent issue from whether or not to hold the emergency funds in a Roth.