muni and corporate bonds?

If your buying Muni's for the tax free income then you should not be putting it in a tax free account. Your defeating the purpose. Now if your buying them for the safety and want to justify that, then that's understanble.

But, to answer your question. When interest rates go up, the price on the bonds will fall. I think they are necessary for a well diversified portfolio but I would not go long term on bonds.

Bonds rates are low, yes, but rates work inversely with value. If the rates start picking up again, bond values drop.

As others have noted, having a muni in a Roth seems not very smart since Roth gains are tax-free anyway. That said, if you wanted to invest in a muni bond issue that people think is risky a Roth might be the place to do it. Detroit general obligation bonds, for example. If Detroit's bankruptcy works out the bonds could jump hugely. Or you could lose everything. That kind of volatile security is what you want in a Roth.