XRP (XRP 2.25%) and Bitcoin (BTC 0.62%) are proven cryptocurrencies that aren't going to go to zero. In the long term, they're more likely to be more valuable than they are today. And they might even be better bets than some assets that people widely consider fairly safe.

So even conservative investors should consider buying and holding them, at least in a modest proportion like a total allocation of about $3,000 between both. Here's the argument for why these coins can be right at home in a lower-risk portfolio.

The case for these two coins being safe enough to buy and hold

Bitcoin and XRP are valuable for different reasons, and the differences matter even more than usual for portfolios that are meant to be safer than average.

XRP is valuable because it's a financial technology that's in active use and development. It aims to outcompete technologies like SWIFT, which is widely used to make international monetary transfers. SWIFT is pricey, and transactions take days to close, and to make matters worse, banks that use it typically need to pay currency exchange fees on top of the transfer fees. If those banks use XRP as a medium of exchange instead, their transfers will close in a few seconds and cost fractions of a penny on average.

Therefore financial institutions have a strong incentive to buy XRP and use it. The larger their international transfer volume, the more they stand to gain -- but the more XRP they'll need to buy. So, as long as there's no other technology that's as cheap and as fast, XRP will continue to see banks shift their capital over time, raising the price of the coin. If the global economy tanks and money stops being transferred between accounts in different countries, all bets are off, but otherwise, XRP's value will, over the long term, most likely increase rather than decrease.

Bitcoin, on the other hand, is valuable today because it is becoming much harder to mine, and thus the supply growth rate is dwindling. It can't be printed like fiat currency, so it may behave as a hedge against inflation. And it isn't useful for much of anything, so it probably can't be displaced by a newer and higher-tech competitor. That means it's very likely to continue to gain in value so long as it can capture a consistent level of demand; it's the same phenomenon as shown in the most basic supply and demand chart in every microeconomics textbook.

What's more, Bitcoin's miners are spread around the world. No single country that has an economic collapse will prevent it from being mined. No single government can ban it. While it's a bit early in the asset's lifetime to fully endorse the idea that it's "digital gold," it does appear to fit Bitcoin on the basis of its enduring appeal. And if the degree of interest from financial institutions is any indication, there's still a lot of capital that's set to flow into the coin, and in all likelihood, stay there for years and years.

There's no need to go overboard with your allocation here

With all of the above being said, conservative investors should dabble in these two assets deliberately rather than firing off a few buy orders and then forgetting about them. Any investment that you overcommit to can feel too risky if its price is volatile, even if over the long term things are likely to work out in your favor.

In practical terms, that means carefully calibrating the percentage of your portfolio's value that you allocate to the two coins to remain fairly low -- an allocation of about 1% to 2% in total is just right. If you're working with $3,000, it makes sense to put about $2,250, or 75% of that allocation into Bitcoin, and the remainder into XRP, because Bitcoin is the safer asset overall. You can always increase your allocation to XRP later if your thinking about its risk profile evolves as you learn more.

Another thing that conservative investors need to appreciate is that XRP and Bitcoin will be volatile; there is no guarantee of buying it at a "good price" at any point in time, and it's challenging to even create such a judgment about value as you might with a stock. So don't commit your capital all at once. Set up a dollar-cost averaging (DCA) plan and slowly deploy your capital in tiny increments over time. The more patient you're willing to be when building your position, the less likely it will be that your cost basis is higher than it needs to be.

The final piece of the puzzle is holding through volatility. In a conservative portfolio, these assets will probably be the single most volatile segment. Don't take that as a sign that your investment isn't going to work out over the long term or that you should sell.

The only way to gain upside is to keep them, even if it's uncomfortable relative to what you're used to.