@OP why store long-term?
Have you ever read and understand the full "Terms & Agreements" that using any stablecoin require?
I mean, you're assuming double risk.
First that FIAT Collapse or it become more worthless.
Second that you violate some rules inside their long long list of condition that you're accepting when using this stablecoins.
Third if you store it in an exchange you are not totally controlling it (and more over they are operating without any legal rules = no complaints!)
Fourth if you store in their wallet, you're just using a centralized coin that can be each time sized, or they can just stop to update = risk to be hacked
Fifth , these are centralized project and they can always mod. their rules and add "taxes" or other tools... I mean you're accepting their rules when start to using their "Product".
etc etc etc.
I am quoting just one T&A (edited) since I don't want to talk about any in particular, but I don't want assume all of these risks for having a not regulated FIAT money in my portfolio. If we are using bitcoin and other crypto is the reason WHY we should try to bypass the classic financial system.
The Times 03/Jan/2009 Chancellor on brink of second bailout for banks
Using stablecoins it's something totally different from using crypto.
XXXX reserves the right to “blacklist” certain USDC addresses and freeze associated USDC (temporarily or permanently) that it determines, in its sole discretion, are associated with illegal activity or activity that otherwise violates the terms of this User Agreement (“Blacklisted Addresses”).
In the event that you send USDC to a Blacklisted Address, or receive USDC from a Blacklisted Address, XXXX may freeze such USDC and take steps to terminate your USDC Account. In certain circumstances, XXXX may deem it necessary to report such suspected illegal activity to applicable law enforcement agencies and you may forfeit any rights associated with your USDC, including the ability to redeem USDC for U.S. Dollars.
XXXX may also be forced to freeze USDC and/or surrender associated U.S. Dollars held in Segregated Accounts in the event it receives a legal order from a valid government authority requiring it to do so.
....
You are aware of and accept the risk of operational challenges. XXXX may experience sophisticated cyber-attacks, unexpected surges in activity or other operational or technical difficulties that may cause interruptions to the USDC Services. You understand that the USDC Services may experience operational issues that lead to delays, including delays in redeeming USDC. You agree to accept the risk of transaction failure resulting from unanticipated or heightened technical difficulties, including those resulting from sophisticated attacks. You agree not to hold XXXX accountable for any related losses.
Last but not least, there are a lot of concerns about the future of these stablecoins (the actual version we are seeing during these days) just to quote one of the last news/analysis that I have read about them...
https://www.ibtimes.com/do-crypto-stablecoins-threaten-financial-stability-2980148