Keep in mind that the interest you get when you cash the bonds is subject to federal income tax. You must report that interest as ordinary income on your federal income tax return and pay tax on it in the year in which you cash it. The only way around this is to swap your bonds for Series HH bonds. In general, that was because of confusion over the rules for how withdrawals would be treated from a tax standpoint. You figure all this out on IRS Form 8606.
Some complex rules apply for figuring out what gets taxed.
Just keep in mind that although the IRS allows Roth IRA conversion amounts and Roth IRA contribution amounts to be held in the same account, your IRA trustee or custodian may not allow it. In other words, trustees and custodians may have their own policies in this regard. If the policy suits you, fine. If not, you can find another trustee or custodian. The problem is that most workers either have no such coverage, or have coverage that they believe is inadequate, according to a survey by the Consumer Federation of American and the American Council of Life Insurers.